I've not shot off a gazillion rockers since stepping up to B.A.T. (straight from 4.12.2 to B.A.T. 4.0), but my impression is that there is a random aim offset applied to a set of rails or tubes, as a group. This offset seems to be of one of two states:
1) All fire pretty much where aimed.
2) Where rail/tube groups are in pairs, one aims high and the other aims low.
Why not any instances where both racks aim low or both aim high? It's ALWAYS one low/one high, or both OK. I presume this is modeling an alignment error for the rails or tubes as a group, because ALL rockets from such a group suffer the same offset.
Furthermore, the degree of offset is rather marked. Estimating from the gun sights reticle, the offset, when present, amounts to about 2 degrees. That's pretty large. Something tells me that in the real world it would be dead easy to ensure no such large alignment error is permitted. A 4 degree total difference in alignment would be easy to see by eye; no measurement apparatus required to detect that!
When the annoying offset occurs, which, again, always has one group going low and the other high, I find that if I go into a 45-60 bank (high rocket, wing low) I can sometimes get a pair fired together to hit at about the distance intended. Instead of one hitting far short and the other sailing off almost into the next county.
I'm going to examine some classes to see what the hell is up...