HSU Research recommends 'near field' sub placement. When I was up there (OC, SoCal) I sat in there listening/audition area and sat virtually next to the sub(s) under test. Still difficult to localize and the 'blend' was good.
If I could work it out, I'd TRY my sub in back of the sofa, concealed (sort of) under the sofa back table. However, I got lucky and near corner placement (3 feet out) and against a long wall made it happen.
I have the advantage, by sheer accident, of having a room with 8 or so walls, 3 45degree corners and an off-center asymmetric ceiling of 12' max and 8' at one side. This room seems to break up or not be conducive to the formation of 'bad' standing waves....(so called peaks or suckouts).
Treatments ARE in the offing, but the idea would be to kill first reflection points from my Maggies and deaden the back of the room....the back wall is a reflection monster, too.
MAAB, please be careful, and Shad, this is meant with all due respect, of any and MOST prescriptive advice. Your listening area is a unique problem and Opportunity.
Experiment around. Even if you can't leave something there due to WAF, try it. Send everyone OUT for the day. Invest in some movie tickets for 'em all. Get RID of them so you can move stuff around and experiment. That's how I discovered, many years ago, that the one hard/fast rule of Magnepans.....IE, tweeters OUT doesn't apply in ALL instances. You will learn stuff nobody could tell you about your room / system / ears / interactions.
It'll all be good.