I no longer have the readme's in my HTC folder for the last few patches and updates, but wasn't there a change to weapons in one of the patches in the last year? I'm fairly certain they changed the GV modelling with regards to weapons and penetration, but were any of the weapons on planes also adjusted?
I think a lot of what happens that seems odd is only perception, however I've had nights where I could kill anything with a single 30mm hit, and others where I've hit the same plane 5 or 6 times, sometimes close enough to kill myself with the blast, without downing the other plane.
Lag could only effect when the other guys takes the damage, not how much of it he takes, so I wonder if there is actually some component that's been changed, or if it really is just the luck of where the round hits that results in no damage, or just an oil leak instead of a catastrophic result.