I'd try putting them on either side, facing in as well as behind the chair facing out, and even on the floor facing up. You'll have to experiment with each to see if any or all of them give you what you are after. To me, ideally, you want surrounds at least a few feet behind you, and if you can't do that, then you will pretty much just have to experiment to find what works best for your specific setup.
Sorry, but the Chucker's rear speaker arrangement looks like a disaster to me.