ob_start chunk_size 0/1 behave differently than any other value <4096

Description

https://3v4l.org/fHmH7

The following code:

<?php

function my_cb( $a ) {
    return $a;
}

ob_start( 'my_cb', 0 );
ob_start( 'my_cb', 1 );
ob_start( 'my_cb', 2 );

$status = ob_get_status( true );
var_dump( array_combine( array_column( $status, 'chunk_size' ), array_column( $status, 'buffer_size' ) ) );

Resulted in this output:

array(3) {
  [0]=>
  int(16384)
  [1]=>
  int(16384)
  [2]=>
  int(4096)
}

But I expected this output instead:

array(3) {
  [0]=>
  int(4096)
  [1]=>
  int(4096)
  [2]=>
  int(4096)
}

PHP Version

8.3.x

Operating System

No response

Start with the PHP documentation for ob_start() and ob_get_status(), then reproduce the linked 3v4l.org example on PHP 8.3. Compare the documented chunk_size and buffer_size behavior for values 0, 1, 2, and other values below 4096. Done means the relevant documentation explains the observed behavior or records a confirmed correction.