Hmn... I've frequently noticed the opposite -- "gun damaged AA," etc. However, they are supposed to cease fire when an ally is in their sights. I edited the dp for some ships last year and they're pelting me big time (especially the BattleCruisers) when I get into their line of fire; the damage profile (for scenery objects these are located in the objects_dp folder) also contains the shooting angles and the 'activation' range (how far away an opponent is before it starts shooting). There are some dp editorials around but, should you try that route, you may still have to play with the dp entries a bit to get the response to your liking.

Other than that, in the case of ground gunnery, you can try my old method of placing more than one unit on the same spot, each facing a different angle.