Google Sheets / Excel quartile if by group

I'd like to calculate where a percentage falls, by quartile, by the size of region. See snapshot of data:

So, I want to know, for small (then medium, then large) regions - does their % of 2-5s fall in the 1st quartile? 2nd? etc. I'm a little lost on how to do this. Any ideas would be greatly appreciated.

My ideal outcome looks something like this (dummy data):

Thanks!