Also if you are able to circle between top-bottom or left-right then the balls get confused and change their direction constantly so easy to kill.
I got that "perfect circle" hitting all 4 corners and really started messing with the pathfinding--it started pulling all of the enemies into the center until a baddie spawned on me and ended my streak. Fun game, and really interesting article on WASM.
Maybe shooting needs a cost associated with it.