Very good read!
A nugget of though reading from some of this:
BoB: While at close range a 7mm would be effective, the fear of getting shot down by bombers defensive mounts kept them a little farther, add to the fear of collision too.
Farther away, more dispersion, fewer hits and less damage if they do hit.
When US bombers where over Germany, the similar can be surmised where German fighters engaged at longer ranges and with less time on target, again for fear of being hit by the storm of .50 flying at them and colliding with another airplane. Naturally this reduced the chance of their shorts hitting, but in this case the 20mm was mainly HE, relying on the explosive effect than the penetrative effect.
I have seen a couple of film clips of B-17's being shot at at point blank, but it is very likely this was a B-17 out of formation with, well, "dead" gun position, so he had little fear and proceeded to unload everything on the helpless bomber.
Hypothesis: the Russians where effective with RCM because they pressed attacks to point blank while most other nation pilot did not. There was more incentive too because for a time it looked like Russia will loose.