I really hate to get into this, because at all but the higher alts the advantage can still be negated by taking your time attacking bombers. However, at high alts, I believe this is the reason they are pretty near impossible to take down.
When steering a bomber from the gunner position, there is no loss of speed. Even complete circles, at about an 80 degree bank, the plane is losing neither speed nor altitude.
A short example in film is posted
here, you can sit in the cockpit and watch the airspeed and altimeters, all steering is done from the gunner positions.
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FattyFat Drunk Bastards"Quit cryin in yer beer, it'll make it go flat."