I think that was the result of Dyson's study - a gunner never saw a fighter so they could just as effectively be removed or repalced with fixed guns.

And in Wald's research a night fighter still had some difficulty finding and approaching abomber even with ground radar - so they fired at it (using proximty fuses or upward firing guns) essentially at random points - there was no statsistical bias of the fighter pilot targetting specific systems