Are there only 2 different sight apertures for the carry handle sights? The one that came with my rifle has a small hole and then when you flip it, it's got an even smaller hole. My brother has a aperture on his AR that has a large hole and a medium hole. Are there more than these 2 apertures? I did some reading and people seem mostly to talk about the A1 and A2 apertures, but I'm not totally clear on which is which.