My tests were done at "veteran" difficulty
1.Place an AH-99 Blackfoot, player as pilot, flying
2.Place an enemy Mi-48 Kajman, flying, at 4-5 km distance from player, facing away from the player
3.Set the behaviour to "COMBAT" for the enemy helicopter (by script or by waypoint)
3.Switch to manual fire, try to engage the chopper

Observed: enemy launches flares at the moment of the launch and successfully decoys the missiles every time
Expected: flares should be launched only when missile is within 2-3km range; missiles should re-lock on target when flares are burnt out.