Thanks Steve, Since this was mostly pre late-1944, the problem was most likely green pilots. I'd bet this situation rapdily changed as they got seasoned ... at least one would HOPE so.
I have seen enough gun camera film to know that estimating range with the film was not an easy task, by any means. You could be right and, if so, then the "real" range was ± quite a bit and this was a case of "armchair quarterbacking" by the intelligence guys as feedback to the pilots. I don't know about any of you but while I was learning to fly, the right altitude for flaring for a landing was something you learned only by doing it. Once you learn, it sort of gets to be second nature and you don't even think about it when you land.
I'd venture to say learning to shoot at an enemy plane would be much the same. I've only done it with lasers in a Beech T-34 but, I learned quickly. It would seem to be the same with bullets ... except for learning the bullet drop and speed difference ... which it seems would be easily learned from shooting at towed targets with the occasional tracer for feedback. I'd bet the same study done in the first quarter of 1945 would have given significantly better results with mostly the newer, green pilots shooting at longer ranges.
But I also don't have the 1945 study to prove that ... just conjecture, which is worth what you paid for it. Thanks for the neat stuff Steve!