in my experience, AH gunsight sizes vary from plane to plane. That is, the distance of your head to the gunsight, and also the size of the polygon which the gunsight sits on both vary. Because of this, no reliable pixels to mils measurements can be made that will work in more than one plane.
I made a K-14 sight that had the rings set to allow me to approximate range by placing the enemy wings within the outer ring and the inner ring. For the P-51, F4U, and P-47, all the bitmaps ended up being differently sized in order to achieve the same effect.
