I would personally drop the rule that AA guns fire at any air unit that flies over, I'm sure they were flying at a high enough altitude that AA guns weren't very effective. And I'm sure they dropped their altitude to bomb their targets. Very simple fix, you just build AA guns on the areas they really worth some PPs, the rest like the French coast will be easily defended with fighter cover, they barely worth anything anyways. I think this way makes a lot more sense, and it's more realistic