Honestly it also has to do with the type of bombers you fight against.
Ju's attack facing bit below the ship. The belly gun can't shoot you neither can the tail guns too.
Lancs attack from the belly up. It has no belly gun which is perfect. At 1k away just go down and gain speed then attack up. If you do that really fast you'll avoid them even noticing you and getting on the nose gun.
B 17s and B 24s are basically flying fortresses. They got guns everywhere. My suggestion is to attack facing them or to the side. Like a Hoe. If you attack from the 6 your a very steady shot whereas from the side your a much harder target where they will more likely waste bullets.
Hope this helps.