Smoke dischargers

[RubberNeck]

What triggers a vehicle to pop smoke? If this is covered somewhere in the manual, forgive me as I was not able to find it. Sometimes a non-penetrating hit will cause defensive smoke, other times a miss will. Is it somewhat random or does it depend on morale and suppression factors? My unscientific research would indicate that a unit will only pop smoke when fired upon by a gun that has a good potential for a kill, but then again this is not always the case.

Dean