Sure would be nice to have trees with which fighters could collide and with which gv's could hide.
Field AAA does need to get some kind of field of view though, having ack fire on my tank when it is below the field (field is raised) and there is no way for the AA to see.. yet it fires into the ground!.
IMO, if field AAA would have some kind of "triangulation without obstacles" kinda logic... say, ack gun gets range on target by triangulating target's range. If the aaa could not get such triangulation because an object (a hill, a tree, a hangar) was in its path then the ack would not "see" it and thus not fire.
To add to that, if the field AA had a "2 second target switch" delay, with which it would take 2 seconds for an ack gun to stop firing at target A and fire at B, things may get a bit better than have a gun instantly stop shooting at someone and instantly send tracers at someone else with such accuracy.
Would be cool to make some AA and flak guns on fields be mannable.