Common sense might suggest, that both antennas should feature about the same signal level.

But in reality, depending on the range of the frequency band, these penetrate walls in a different manner, which would need to be considered, when comparing AP distance measurements. Without indoor location or alike, too many parameters remain unknown. Otherwise one would know when two AP share almost the same GPS fix, with eg. 25cm difference into on direction. When two AP are stacked on top of each other, how would you tell them apart, except Z axis?

How about: https://en.wikipedia.org/wiki/Wi-Fi_positioning_system ?