Towards the end of Aces High 2 I got pretty good at ground and bomber defensive gunnery (in my opinion). Most of it is lost when I returned to AH3 after a break. One tip is to look at the film recording when you still remember where you aimed and see from enemy view where tracers go. I stopped playing with zoom and although used it on some occasions, instead tried to use consistent setting that would suit me most occasions.
I only used stock gunsights and no overlays. Gunsight for initial lead position, fired couple of tracers longer out than max range so tracers and aircraft would meet at max range or so, then raised my head clear and kept fixated on the target and made corrections based where target and tracers met. Peripheral vision shows you the tracer stream. Correcting via tracers gets complicated when there are a lot of other guns firing.
I had found a document online that discussed using tracers similar to the following video (without the bottle of Guinness Stout though), but lost it.
There were some simple thumb rules how to correct fire with descending targets etc and something about tracers rising up or lowering down and a diving target.
As a gamey tactic I sometimes aimed a high rate of fire weapon with a mouse and shook it a little to give wider dispersal.
