Stickies don't need to make actual contact, as long as they get close enough. This "stickiness" (I don't think it's a hitbox, dormant nades won't explode if you shoot right next to them) feels reduced in 4. I think nades in general are slower, too, which is why they don't go as far. I haven't noticed any artificial arcing outside of campaign.
Before all else you must build muscle. Then you must become hero to children everywhere.
My main plasma problem is the opposite. I'll stick someone, and it'll be on their leg or something, and explode, but nothing happens to the enemy. It might as well have flown 50 ft. behind them because it has no effect at all. This is rare..only happened about 5 or 6 times to me, but it's still really annoying, especially when you're kind of depending on that grenade, and it just teases you.
Most likely this is also a lag issue, and the grenade didn't really stick the guy at all, but it sure is irritating.
I am the rocks of the eternal shore...crash against me and be broken! GT: Deadly Mantodea