The way I read RAW a minion group affectively is a single target that fight as one. I mean if it's a group of 4 minions it makes no difference if you attack minion 1 or minion 3 it goes to the same pool.
So how does grenades work? I mean on one hand it's a grenade with blast so realistically it seems like it would hit all of them.. However, mechanically it seems way too powerful because you only apply soak once. A grenade blast 6 because of single soak applied could wipe out a minion group of 6 or more since they fight as one and are bunched up.
Thoughts?