Speaker distance

If you sit on a high back chair / couch, it will block some rear reflections. Having the speakers toed about a foot wide of the ear helps with this as it uses the back of the chair / couch (instead of rear wall) for reflection. I have wide dispersion speakers for mixed movie/music and have it toed 3 feet wide of center as a balance for multiple seating.

There are mathematical ways for determining acoustical properties (Bostons Symphony Hall was built this way) but you'd probably need to hire a team of architects to design you a new home. So I'd just recommend trial and error. Personally, I own five and a half feet tall Quad Electrostatics and the recommended distance from the rear wall is thirteen feet with side clearance. I've found that nine feet sounds the same to me. However, given that they're not pushing air, I can sit fairly close to them if I want. 

Forgot to mention, corner traps and sound panels might help.

I’m in a rectangular room.  My speakers are 4’ off the front wall, 3’ from the side walls and a little less than 8’ apart.  My head is 8’ from my speakers, with ears in line with the tweeters. The back wall is about 7’ behind my head.

@aewarren , this is the correct response 

There is only one sure way to optimize speaker positioning in a room and it is by ear.