Speaker distance

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.

For a sealed design, the equilateral triangle or similar usually works great. Add a port, and the room interaction multiplies. For planers, it becomes even more complicated. 
 

I am sometimes surprised as to how the rules can be broken to good effect. In college, one year I set up my double Advents about two feet from my mattress (which was on the floor). I used to listen at night in my bed, my head two feet from the plane of the speakers, which were about 8 feet apart. It was immersive and holographic, with substantial sense of depth (my Marantz 7 preamp helped give the depth, along with my Ampzilla).