Spitfire/Hurricane reflector gunsight

forgive my inabillity to use correct terminology here guys, but here we have an image where our wingspan setting is set to 32 ft, 1 click, for the 109. next quuestion is what distance to object setting do we use to establish the correct diameter of the circle. 1C has set this diameter at the closest range to object 150 yds. so in relation to the pictures from the movie, and or the video in post#1 what is an accurate distance to object setting for both those real life images ???

edit im reading that this ring is some sort of cross-firing solution ring. 100mph / 50 mph ???? which adds a whole new angle upon the subject.. thanks to bigpickle for digging that up.