Consider it that the fighter escorts would have peeled away before they get to the actual facility (lack of range and/or their job of defending the bombers against interceptors is already acomplished so no need to risk going down from AA gun fire as well).
Thinking of it like that makes sense to me. Interceptors would be intercepting as far AWAY from the facility as they possibly can, while the AA gun is fixed AT the facility.
Not to mention that AA flak is rather indiscriminate. If it were firing on the escort, it would be firing on the interceptors as well, and the dogfight would be occuring in the thick of the flak. And that’s not what the defender would want to do (and it would suck in the game cause the defender might lose more than the attacker due to friendly fire). Especially since it’s the escorts duty to peel the interceptors away from the bombers and NOT keep the dogfight in the same area.
Yes, I was going to go into a much more detailed explanation including all this but time was a restraint (I was at work when I made that reply).
Really, it just makes sense if you think about it. 🙂
If your (fixed position) AA guns are firing into the skies, it’s too late to scramble interceptors as this means the bombers are already over their targets AND you’d hit your own interceptors just as often as you’d hit the enemy bombers. Escorting fighters would have turned back before entering AA gun range so as to mitigate losses (once the bombers are over their target, no need to risk losing extra fighters that aren’t going to help out in the raid)! AND, once the bombers are dropping their payload, what’s the point of intercepting them anyway as the damage is already done!