I fly the 190A5 primarily. Both this bird and the Dora get bouncy when I'm in a fight with the Forward tank full. I always change tanks and burn the Forward down to 50%, then shift to the drop tank. In the Butcher Bird this creates a much more stable firing platform. Can't say for other planes, but it works here.
Also, turn your tracers off. Most sticks end up watching their tracers and aim by spraying a fire hose. That isn't aiming, that is guessing after the fact. You end up trying to 'walk' your fire hose into the target. By turning tracers off you have to give a great deal of thought to lead, aim points, etc. At first your aim will drop dramatically, though you will suddenly figure it out and get much, much better.