Maplegrovemusic,
The general rule of thumb is a minimum of 3' behind the speakers, a minimum of 2' on either side. But 5' is better behind and they keep getting better up to 15'! They really like to breathe.
To put this in perspective, you want the tweeters on an equilateral triangle with you, or a bit less, it will vary with room and preference. And you don't want to be too close to the large ones, because a) it will boost the bass and b) you'll start to hear the angular separation between the woofer, mid, and tweeter.
Another thing you have to consider is that the big ones can make a small room inconvenient and claustrophobic.
Unfortunately, there are no precise guidelines. I think it helps if you can equalize the bass, as the speakers grow large with respect to the room the room starts to act like a sealed enclosure and the bass output goes up. Which can be good or bad depending, but in any case can be tamed with EQ.