idk. it sounds simple but it makes it hugely effective (or AA very ineffective). there's also the issue of what happens when you move AA into the target area before the plane hits.
In my opinion, every plane should be a single pass in the style of CAS, rather than a loitering strike. It would make things more deterministic (which I'm a fan of). In which case, the strike would hit as normal if you moved the AA into the zone after the plane has shown up, but the window would be so small it wouldn't "really" matter much in terms of looking weird.
You could still make AA function as normal and try to shoot down loitering planes if you decide you want to keep loitering (conceptually), but then still have the AA gun's "zone of control" being the small (or large depending on the specific gun I guess) radius around it being a safe zone that the enemy can't summon the planes towards.
The main thrust of the idea here is really to make airstrikes and AA sort of complementary mechanics that are part of the core game. Currently the interplay between them is, to be frank, garbage. You could even, in theory, make a small air-strike or bombing run or something part of a faction's core tech tree as long as other factions had the tools available to protect themselves from it in theory, which could be interesting.
If you want to take a case study for why I think this might be useful, stuff like the Pak43 would be actually somewhat resilient even in its current form
as long as it was supported by anti-aircraft units. But an unsupported stationary emplacement would be child's play for an allied bombing run otherwise. The counterplay options might consist of the AA units being relatively fragile, and a raid with armor is targeted at dislodging or destroying the AA gun, which then allows them to instantly hard counter the Pak43 without its support.
Similarly, on-map artillery (should there be any? That's another question we might actually be able to discuss!) could be defended from the two-click recon-stukka counter, which imo is very frustrating when whole doctrines become useless because of the CAS meta. Rather than just making them so tough they can withstand a 50kg bombing run, you give the allies options to allocate extra resources to defending these vulnerable positions, at the expense of spending resources elsewhere.