diff --git a/lib/api_aggregate.php b/lib/api_aggregate.php
index fba05ff3ae..25fd11f1b0 100644
--- a/lib/api_aggregate.php
+++ b/lib/api_aggregate.php
@@ -409,20 +409,20 @@ function aggregate_graphs_insert_graph_items(int $_new_graph_id, int $_old_graph
 					$prepend = false;
 					$prepend_cnt++;
 				} elseif (str_contains($save['text_format'], ':current:')) {
-					if ($_total_type == AGGREGATE_TOTAL_TYPE_ALL || $_total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
-						// All so use sum functions
+					if ($_total_type == AGGREGATE_TOTAL_TYPE_ALL) {
 						$save['text_format'] = str_replace(':current:', ':aggregate_sum:', $save['text_format']);
+					} elseif ($_total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
+						$save['text_format'] = str_replace(':current:', ':aggregate_current:', $save['text_format']);
 					} else {
-						// Similar to separate
-						$save['text_format'] = str_replace(':current:', ':current:', $save['text_format']);
+						cacti_log(__FUNCTION__ . ' unhandled total_type ' . $_total_type . ' for :current: in text_format', true, 'AGGREGATE', POLLER_VERBOSITY_DEBUG);
 					}
 				} elseif (str_contains($save['text_format'], ':max:')) {
-					if ($_total_type == AGGREGATE_TOTAL_TYPE_ALL || $_total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
-						// All so use sum functions
-						$save['text_format'] = str_replace(':max:', ':aggregate_sum:', $save['text_format']);
+					if ($_total_type == AGGREGATE_TOTAL_TYPE_ALL) {
+						$save['text_format'] = str_replace(':max:', ':aggregate_sum_peak:', $save['text_format']);
+					} elseif ($_total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
+						$save['text_format'] = str_replace(':max:', ':aggregate_current_peak:', $save['text_format']);
 					} else {
-						// Similar to separate
-						$save['text_format'] = str_replace(':max:', ':max:', $save['text_format']);
+						cacti_log(__FUNCTION__ . ' unhandled total_type ' . $_total_type . ' for :max: in text_format', true, 'AGGREGATE', POLLER_VERBOSITY_DEBUG);
 					}
 				}
 			}
@@ -1428,14 +1428,14 @@ function aggregate_handle_ptile_type(array $member_graphs, array $skipped_items,
 								$pparts = explode(':', $parts[1]);
 
 								if (isset($pparts[3])) {
-									if ($_total_type == AGGREGATE_TOTAL_TYPE_ALL || $_total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
-										// All so use sum functions
+									if ($_total_type == AGGREGATE_TOTAL_TYPE_ALL) {
 										$pparts[3] = str_replace('current', 'aggregate_sum', $pparts[3]);
 										$pparts[3] = str_replace('max',     'aggregate_sum_peak', $pparts[3]);
-									} else {
-										// Similar to separate
+									} elseif ($_total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
 										$pparts[3] = str_replace('current', 'aggregate_current', $pparts[3]);
 										$pparts[3] = str_replace('max',     'aggregate_current_peak', $pparts[3]);
+									} else {
+										cacti_log(__FUNCTION__ . ' unhandled total_type ' . $_total_type . ' for pparts[3] in text_format', true, 'AGGREGATE', POLLER_VERBOSITY_DEBUG);
 									}
 
 									switch($pparts[3]) {
@@ -1510,14 +1510,14 @@ function aggregate_handle_ptile_type(array $member_graphs, array $skipped_items,
 								$pparts = explode(':', $parts[1]);
 
 								if (isset($pparts[3])) {
-									if ($_total_type == AGGREGATE_TOTAL_TYPE_ALL || $_total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
-										// All so use sum functions
+									if ($_total_type == AGGREGATE_TOTAL_TYPE_ALL) {
 										$pparts[3] = str_replace('current', 'aggregate_sum', $pparts[3]);
 										$pparts[3] = str_replace('max',     'aggregate_sum_peak', $pparts[3]);
-									} else {
-										// Similar to separate
+									} elseif ($_total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
 										$pparts[3] = str_replace('current', 'aggregate_current', $pparts[3]);
 										$pparts[3] = str_replace('max',     'aggregate_current_peak', $pparts[3]);
+									} else {
+										cacti_log(__FUNCTION__ . ' unhandled total_type ' . $_total_type . ' for pparts[3] in value', true, 'AGGREGATE', POLLER_VERBOSITY_DEBUG);
 									}
 
 									switch($pparts[3]) {
diff --git a/tests/Unit/AggregatePtileFormatIntegrationTest.php b/tests/Unit/AggregatePtileFormatIntegrationTest.php
new file mode 100644
index 0000000000..e94bcee4e7
--- /dev/null
+++ b/tests/Unit/AggregatePtileFormatIntegrationTest.php
@@ -0,0 +1,229 @@
+<?php
+/*
+ +-------------------------------------------------------------------------+
+ | Copyright (C) 2004-2026 The Cacti Group                                 |
+ |                                                                         |
+ | This program is free software; you can redistribute it and/or           |
+ | modify it under the terms of the GNU General Public License             |
+ | as published by the Free Software Foundation; either version 2          |
+ | of the License, or (at your option) any later version.                  |
+ +-------------------------------------------------------------------------+
+ | Cacti: The Complete RRDtool-based Graphing Solution                     |
+ +-------------------------------------------------------------------------+
+*/
+
+/*
+ * Integration tests for aggregate 95th percentile format string replacement.
+ *
+ * These tests simulate the full COMMENT and HRULE processing pipeline in
+ * aggregate_handle_ptile_type(): explode the pipe-delimited string, replace
+ * pparts[3], and rejoin. This verifies that the fix produces correct
+ * rrdtool variable references for SIMILAR vs ALL total types.
+ *
+ * The bug: SIMILAR was grouped with ALL, causing aggregate graphs to use
+ * aggregate_sum (sum of in+out) instead of aggregate_current (per-source)
+ * for 95th percentile, roughly doubling the displayed value.
+ *
+ * See: https://github.com/Cacti/cacti/issues/6835
+ *
+ * SYNC WARNING: process_ptile_pparts() and process_text_format() below
+ * replicate logic from lib/api_aggregate.php (lines ~412-427, ~1430-1439,
+ * ~1512-1521). Production functions require DB/session state that prevents
+ * direct invocation in unit tests. If the production replacement logic
+ * changes, these helpers must be updated to match.
+ */
+
+require_once dirname(__DIR__) . '/Helpers/CactiStubs.php';
+require_once dirname(__DIR__, 2) . '/include/global.php';
+
+/**
+ * Simulates the full COMMENT/HRULE pparts processing pipeline from
+ * aggregate_handle_ptile_type(). Takes a pipe-delimited text_format or
+ * value string, applies the total_type replacement on pparts[3], and
+ * returns the reassembled string.
+ */
+function process_ptile_pparts(string $value, int $total_type): string {
+	$parts = explode('|', $value);
+
+	if (!isset($parts[1])) {
+		return $value;
+	}
+
+	$pparts = explode(':', $parts[1]);
+
+	if (!isset($pparts[3])) {
+		return $value;
+	}
+
+	if ($total_type == AGGREGATE_TOTAL_TYPE_ALL) {
+		$pparts[3] = str_replace('current', 'aggregate_sum', $pparts[3]);
+		$pparts[3] = str_replace('max',     'aggregate_sum_peak', $pparts[3]);
+	} elseif ($total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
+		$pparts[3] = str_replace('current', 'aggregate_current', $pparts[3]);
+		$pparts[3] = str_replace('max',     'aggregate_current_peak', $pparts[3]);
+	}
+
+	$parts[1] = implode(':', $pparts);
+
+	return implode('|', $parts);
+}
+
+/**
+ * Simulates the full text_format replacement pipeline from
+ * aggregate_graphs_insert_graph_items(). Handles :current: and :max:
+ * substitutions based on total_type.
+ */
+function process_text_format(string $text_format, int $total_type): string {
+	if (str_contains($text_format, ':current:')) {
+		if ($total_type == AGGREGATE_TOTAL_TYPE_ALL) {
+			$text_format = str_replace(':current:', ':aggregate_sum:', $text_format);
+		} elseif ($total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
+			$text_format = str_replace(':current:', ':aggregate_current:', $text_format);
+		}
+	} elseif (str_contains($text_format, ':max:')) {
+		if ($total_type == AGGREGATE_TOTAL_TYPE_ALL) {
+			$text_format = str_replace(':max:', ':aggregate_sum_peak:', $text_format);
+		} elseif ($total_type == AGGREGATE_TOTAL_TYPE_SIMILAR) {
+			$text_format = str_replace(':max:', ':aggregate_current_peak:', $text_format);
+		}
+	}
+
+	return $text_format;
+}
+
+// --- COMMENT pipeline: SIMILAR produces per-source percentile ---
+
+test('COMMENT pipeline: SIMILAR current produces aggregate_current', function () {
+	$input  = '95th Percentile|nth_percentile:95:traffic_in:current';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->toBe('95th Percentile|nth_percentile:95:traffic_in:aggregate_current');
+});
+
+test('COMMENT pipeline: SIMILAR max produces aggregate_current_peak', function () {
+	$input  = '95th Percentile|nth_percentile:95:traffic_in:max';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->toBe('95th Percentile|nth_percentile:95:traffic_in:aggregate_current_peak');
+});
+
+test('COMMENT pipeline: ALL current produces aggregate_sum', function () {
+	$input  = '95th Percentile|nth_percentile:95:traffic_in:current';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_ALL);
+
+	expect($result)->toBe('95th Percentile|nth_percentile:95:traffic_in:aggregate_sum');
+});
+
+test('COMMENT pipeline: ALL max produces aggregate_sum_peak', function () {
+	$input  = '95th Percentile|nth_percentile:95:traffic_in:max';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_ALL);
+
+	expect($result)->toBe('95th Percentile|nth_percentile:95:traffic_in:aggregate_sum_peak');
+});
+
+// --- HRULE pipeline: same replacement pattern ---
+
+test('HRULE pipeline: SIMILAR current produces aggregate_current', function () {
+	$input  = '#FF5722|nth_percentile:95:traffic_out:current';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->toBe('#FF5722|nth_percentile:95:traffic_out:aggregate_current');
+});
+
+test('HRULE pipeline: SIMILAR max produces aggregate_current_peak', function () {
+	$input  = '#FF5722|nth_percentile:95:traffic_out:max';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->toBe('#FF5722|nth_percentile:95:traffic_out:aggregate_current_peak');
+});
+
+test('HRULE pipeline: ALL max produces aggregate_sum_peak', function () {
+	$input  = '#FF5722|nth_percentile:95:traffic_out:max';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_ALL);
+
+	expect($result)->toBe('#FF5722|nth_percentile:95:traffic_out:aggregate_sum_peak');
+});
+
+// --- SIMILAR must never produce summed values ---
+
+test('SIMILAR COMMENT never produces aggregate_sum for current', function () {
+	$input  = '95th Percentile|nth_percentile:95:traffic_in:current';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->not->toContain('aggregate_sum:')
+		->and($result)->not->toContain(':aggregate_sum');
+});
+
+test('SIMILAR HRULE never produces aggregate_sum_peak for max', function () {
+	$input  = '#FF5722|nth_percentile:95:traffic_in:max';
+	$result = process_ptile_pparts($input, AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->not->toContain('aggregate_sum_peak');
+});
+
+// --- text_format pipeline: full string with ISP billing context ---
+
+test('text_format: SIMILAR with :current: in bandwidth label', function () {
+	$result = process_text_format('95th In :current: bps', AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->toBe('95th In :aggregate_current: bps');
+});
+
+test('text_format: SIMILAR with :max: in bandwidth label', function () {
+	$result = process_text_format('95th Peak :max: bps', AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->toBe('95th Peak :aggregate_current_peak: bps');
+});
+
+test('text_format: ALL with :current: in bandwidth label', function () {
+	$result = process_text_format('95th Total :current: bps', AGGREGATE_TOTAL_TYPE_ALL);
+
+	expect($result)->toBe('95th Total :aggregate_sum: bps');
+});
+
+test('text_format: ALL with :max: produces aggregate_sum_peak not aggregate_sum', function () {
+	// This is the secondary fix: ALL+max was using aggregate_sum instead of
+	// aggregate_sum_peak, mismatching the COMMENT/HRULE paths
+	$result = process_text_format('95th Peak :max: bps', AGGREGATE_TOTAL_TYPE_ALL);
+
+	expect($result)->toBe('95th Peak :aggregate_sum_peak: bps')
+		->and($result)->not->toContain(':aggregate_sum:');
+});
+
+// --- Edge cases ---
+
+test('pparts with no pipe delimiter returns unchanged', function () {
+	$result = process_ptile_pparts('no pipes here', AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->toBe('no pipes here');
+});
+
+test('pparts with fewer than 4 colon parts returns unchanged', function () {
+	$result = process_ptile_pparts('label|nth_percentile:95:traffic_in', AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($result)->toBe('label|nth_percentile:95:traffic_in');
+});
+
+test('unknown total type leaves pparts unchanged', function () {
+	$input  = '95th Percentile|nth_percentile:95:traffic_in:current';
+	$result = process_ptile_pparts($input, 99);
+
+	expect($result)->toBe($input);
+});
+
+test('unknown total type leaves text_format unchanged', function () {
+	$result = process_text_format('95th :current: bps', 99);
+
+	expect($result)->toBe('95th :current: bps');
+});
+
+// --- Inbound vs Outbound: verify both data sources handled independently ---
+
+test('SIMILAR handles traffic_in and traffic_out independently', function () {
+	$in_result  = process_ptile_pparts('In|nth_percentile:95:traffic_in:current', AGGREGATE_TOTAL_TYPE_SIMILAR);
+	$out_result = process_ptile_pparts('Out|nth_percentile:95:traffic_out:current', AGGREGATE_TOTAL_TYPE_SIMILAR);
+
+	expect($in_result)->toBe('In|nth_percentile:95:traffic_in:aggregate_current')
+		->and($out_result)->toBe('Out|nth_percentile:95:traffic_out:aggregate_current')
+		->and($in_result)->not->toBe($out_result);
+});