Generally speaking, I've found that stacking slows in certain areas creates a sort of "death zone" for creeps. See this; http://forums.eletd.com/topic/95222-placement-convention/. Specifically, area 5 and path C are great locations to smash creeps with slow.

The scoreboard is about single target...for now. We will be making significant changes soon to address a variety of concerns. Ultimately, slow stack builds should have a chance at scoring well.