Andy, that is an extremely useful and enlightening link, thanks. The pictures and diagrams are excellent, especially the ones that compare the shot pattern of 300 yard convergence at various ranges.
My gunnery appears to be improving with practice in AH, which is not surprising. I find I do better with the P-51 than the Spit, again not surprising considering the greater bullet density of the shot pattern. I've nearly given up on high-angle shots, though. Instead, I try to set up a low-angle shot by varying my pursuit curve, using the Lead-Lag-Pure sequence. AH keeps you a bit more honest than the other sims I've tried.