Anterior pelvic tilt?

Hey guys, I’ve been lurking on this forum for a bit and came across a few threads dedicated to the topic but I never really understood it.

APT apparently hides your “True height” because of the bend of your pelvis and consequently your lower back.

But shouldn’t standing straight I.e standing to get your height taken (with your glutes flexed and abs sucked in)  give you your true height anyway?

Or is this more of a case of your muscles overcompensating and pulling you down I.e you physically CAN’T stand straight with APT?

I’ve already tested that, I actually shrink like 1/4 inch whenever I stand straight compared to when I’m standing as tall as I can with a noticeable curve. Idk why