Given the extent of the issues with collision detection (see the maps thread for some discussion about it) I doubt that DFA will work properly until those issues are addressed. The only thing I am fairly certain about is when air units collide, the collider (that is, the one with more speed at the time of contact) will suffer the suicide penalty, and the collidee (that is, the guy getting hit) usually gets the kill creditation. This may be a bug, but I think it does a great job of inhibiting "ramming" as many air units in multiplayer games ala Battlefield will witness.