Just to offer another viewpoint...
The distance you sit from the rear wall isn't really going to change the reflections bouncing off the rear wall. With this in mind, you are simply going to move the fundamental boundary cancellation to a lower frequency, which ultimately is going to make the issue more audible. Even if you move forward 10 feet (which doesn't look possible in this room), you're still going to be within the Haas window. I would much sooner pin your head against the rear wall, which will result in you not hearing any difference between the direct and reflected sound. I would only recommend moving forward if it also involved adding acoustical treatment to the rear wall.
http://www.peavey.com/support/techno...ncellation.cfm
As far as the mains in the cubby hole...how far is the listening position from the speakers? I would suggest the configuration in your picture, but toe-ing in the speakers to reduce early reflections off the side wall (even if it means making the axis fo the mains cross in front of the listening position). You'll have to play around with trading HF extension at the listening position for less comb-filtering due to reflections off the side walls. But since you're sitting so far back in the room, I don't think you're going to be able to avoid early reflections...so again, acoustical treatment along the side walls would be beneficial too. (it's interesting to note that you can achieve more toe-in by moving the listening position forward....)
As far as optimal subwoofer placement - this is going to depend on the modal distribution in the room. Moving the subs as little as an inch can have a dramatic influence on the dips and peaks you see at the listening position (likewise, moving the mic a few inches can have a dramatic effect too).
http://www.ethanwiner.com/believe.html
I've gotta run, but just wanted to mention that it's a huge system of compromises and you'll have to choose your poison. Every room and application is going to be slightly different...