In the current MA there's almost no reason for field capture minded players to shoot others down, except when defending a base, e.g. beeing vulched while upping to kill the goon. But not even shoot down those that are trying to rtb, or they'll be back twice as fast.
When attacking it isn't a good idea to attack nme ac either, except when vulching. This kind of fight requires 'enough' players on the attacking side, and is boring for the defenders, too.
If the attackers don't have the numbers to keep the enemy planes from the target field down by vulching, it is a bad idea to kill them when trying to take the field anyway. If they're dead, and won't get vulched to often, they'll take off again. When they do, they're the biggest threat because they're close to the town - killing goons. Better tactic is to let them live, chase them, let them chase you, make them fight, but make them fight somewhere else than low over the town. This rewards good flying with a field capture, but not with kill marks on the plane.
The only solution to this I can think of (if adding a respawn timer is not an option) is to move the tactically/strategically (which? someone please give a definition of these terms) most valueable targets (currently: towns of airfields) away from the fields. This can be done in two ways:
a) Move the towns away from the fields. Maybe even add a few more towns to the fields, in the direction of every other field, half way there. If one town is captured, the field changes sides (and all other towns of that field, too). This also would allow GV battles between the towns. Furballs would no longer be over fields (vulching one side) but between them.
b) add something between the fields, which ensuresa field capture, if one side manages to keep airsuperiority in that area. this could be a vehicle base (maybe add a town, so that it's not that easy to capture), but GVs should spawn very close to the airfields, maximum 2 minutes driving time. This would move the fights to the vehicle bases (maybe disable GV spawn at the hangar, forward spawnpoints only, no GV spawnpoints TO the vehicle field), so if one side manages to keep enme fighters away for 15 minutes (respawn time of the vh), it is almost certain that the airfield will be captured, too. Like a) there would be no reason for vulching and fights develop between the airfields.