ESP32 v1.20.0 custom builds failing - memory overlap errors

[imlarry]

I'm building a custom MicroPython v1.20.0 firmware for ESP32-WROOM-32E to freeze modules for a BT gateway. Official firmware (dwnload from website) works fine, every custom build crashes.

Error:
E (57) esp_image: Segment 0 0x3fff0018-0x3fff1260 invalid: overlaps bootloader data
E (57) boot: Factory app partition is not bootable

Tried:
ESP-IDF v4.4.4 (first attempt) - "Segment 0 overlaps bootloader data"
ESP-IDF v4.2.4 (matches official firmware strings) - same overlap error
ESP-IDF v4.0.2 (matches CI) - "Segment 0 end address 0x3fff001c too high (bootloader stack limit)"

The issue: Official firmware loads at 0x3fff0030, my builds try 0x3fff0018 and hit bootloader memory.

What controls segment load addresses? Official builds work, mine don't - same source, same ESP-IDF versions. Missing some config or toolchain difference?

I need frozen modules working for memory savings on this project otherwise I'd just say "mpy-cross and take the hit on the (lots of) strings."

Any clues on what the actual dev env beyond what comes in the git appreciated.

[imlarry]

Oh dang .. this is a total "dho!" on my part.
I had the wrong bin (firmware.bin instead of micropython.bin) on the flash (and kept doing so over and over again) ... didn't figure out the issue until an esptools image_info showed that firmware.bin is a bytewise copy of bootloader/bootloader.bin