I am not sure whether ATC speakers are best set up with little or no toe-in, and perhaps current ATC owners can advise. If sound is little direct, you may want to try as little toe-in as possible.
In a large space you will not notice much effect from toe-in (as they have wide even dispersion) - so just point the straight out and you'll generally get the widest sweetspot and smoothest in room response (think of your speakers as two floodlights and you want to evenly light up your room). I would suggest experimenting with toe-in if they are placed close to side walls (3 feet or less) - to reduce the amplitude of early reflections (best to keep near reflections at least 3 feet from a speaker).
Ryder has some excellent points - where you sit and how close the speakers are to the side walls is very important for the soundstage and image. A really small space suggests using a diagonal configuration with listening chair roughly 6 feet back from the plane of the speakers (avoiding the middle of the room - don't sit in the exact middle). I can't emphasize enough the importance of space around the listener.