I've tried almost everything with no results. It seems we need direct hits to knock anything and without a precisse gunsight I can't do anything but close and ineffective hits.
Seeing some videos with P38s attacking with rockets, it seems those weapons drops too early in AH and the warhead is too weak. One of those videos shows a 90 degrees attack to a troop transport train, that train seems very "small", so I think the distance is about 600 meters or more, the hits were very very precise and the explosions where "enormous".
My question is the next. Rokets are stabilized by little tail wings, and they have self-propulsion for several seconds, in fact they are much faster than the launching plane. The launching plane can go straight to the target without compensing with joy, so, if you dont break, your own plane should hit the target (at hi speeds and well trimmed) but the faster and lighter rockets drop just after fired, in most of the cases you'll lost them under your nose.