How to use @filter correctly

[plechev-64]

PHP Version: 8.1
OS: Ubuntu

Hi, I try to test my custom rule with using @filter, like this:

function f()
{
    /**
     * @warning params of request without any check
     * @filter $_POST ^_POST$
     */
    $x = $_POST[$paramName];
}

but i find in result of test:

$x = $a['f']; 
$x = $_GET['test']; 
$x = $_REQUEST['test']; 
$a = $_POST['test']; 

i am waiting for only this

$a = $_POST['test']; 

why i have unexpectable results?
Thanks!