3 ideas:
1. Do the AA shots as normal (exempting Airborne units). Then ‘reset’ the AA’s for a second phase vs the paras. It may let some AA guns fire twice, but it can be justified by trying to keep things simple and by how slow transport planes are.
2. The defending assigns his shots to 2 categories: planes and paras. Defender has 2 AA guns, attacker has 7 planes and 2 paras. The defender says “I’m gonna shoot 5 dice vs planes and 1 vs paras”. The beauty of this idea is that the defender will really only choose planes (so it is similar to exempting paras), but at least this way he has the option and he can still fire at the attacker if the attacker sends paras but no aircraft.
3. The simple plan. We take a page from the transport rules. Paras are chosen last. This elminates the unrealistic paradrop on the next door territory you could have walked into and stops them from being ‘fighter insurance’. I think this idea is the easiest to implement and it follows precedent.
This solution gives the defender a bit more of a balance (vs the paras ability to cross oceans with no transport) as the para units could activate more AA shots if the defender has a surplus of AA guns. This will keep a power with paras from going too nuts with them. For example, the attacker will not send 6 paras (which is a really unrealistic amount) and a fighter into a territory with 2 aa guns as the odds say fighter is gonna get hit. A player will think twice about heavy para use on a territory that is fortified with aa as it will cost them in escorts–-also realistic. But in most cases, only one or two airbases will be in range, and the defender will rarely have a surplus of AA guns. What I am eliminating here is a late war sleaze move where the USA has taken all western Europe and uses several airbases in territories there to invade germany (which is adjacent), just to block their AA. If they tried that with this rule, all they would accomplish is maximizing Germany’s AA shots. So instead, that will attack by land, and maybe fly in the odd para to actually use as a land unit.