It seems like only Machineguns and sniper rifles do supression in this game.
SMGs and rifles should also do some supression, specially when its several shots in a row in the same vicinity.
A system where supression becomes an acumulative thing with a minimum and a maximum value would be ideal, IE you do near nothing with a single SMG shot, but you do some more supression with a burst of bullets, or with a long amount of automatic fire. Some supression from rifles would be nice too, as a single rifle bullet is generally about as powerful as a single MG bullet in each faction.