Like Dan, mine is located in the front right corner, 5" from the front wall and 5 1/2" from the right side wall. (HT/family room 20' x 30' w/10' high vaulted ceiling)
**NOTE: Because my website is 'free', hosted by GeoCities, if too many HT enthusiasts visit, GeoCities will shut it down for an hour or so because it exceeded the specified 'freebie' Data Transfer Rate. Sorry about that, just bookmark it and visit my site an hour later or when everyone has gone to bed!
Phil
I don't know if I would call it "optimal," but mine is 10 inches from the rear wall and six inches from the side wall. It was a bit closer, but I pulled it out because the bass seemed a bit "boomy" at some frequencies.