Squat Mobility! How Much?

I’m curious as to how much mobility is really necessary to safely squat and make progress. I’m 6ft tall and have unfortunate body proportions that restricts me from squatting comfortably and naturally. Therefor, I squat with oly shoes(thanks to elevated heels). With the shoes, I am mobile enough to squat ATG comfortably. However, there is one movement that I CANNOT seem to perform and it bugs me. That is the overhead squat with narrow grip.