At the moment I choose "fire at will,fire at med.range (poor gunners),fire at fighters (no effect at all on bombers),fire at closing targets" (sometimes a plane can fly by and not see me,holding fire on them could maintain stealth for a while).
Its clear sometimes that there is a problem somewhere,as often the planes are in ideal shooting positions (bang astern sometimes),and the guns just won't open up,I need to manually order them with the binos when that happens