As previously mentioned, the surround speakers should be on the side walls facing each other and should be directly to the side or sightly behind (which you don't have room for). Many with this setup like the sound best when the surround speakers are up high, like around 6 feet, angled down slightly so the speakers point to a spot in space above the primary listening position. You don't want to point them directly at your ears as you are wanting an "indirect" sound from the surround speakers.
Also, it is very unlikely that the back corner of the room will be the ideal spot for the sub - corners usually create the most room reinforcement and you will get a lot of "hot" and "cold" spots where the bass is doubling up or cancelling completely because of standing wave reinforcement and cancellation.
2-Ch (HT L/R): Oppo BDP-105 BD, Adcom GFP-750 pre, Bryston 10B Sub Xover, Bryston 4BSST2 / Paradigm Signature S4 v.2 (L/R), (2) SVS SB12-NSD (Subs)
Home Theater: Bryston 4BSST2 amp / Paradigm CC-590 (C), Outlaw 7700 amp / (4) Def Tech UIW-RSSII (LS/RS/LB/RB), Samsung 46” 3D LCD