I have a similar problem, having a hexagonal living room, where one wall has a fireplace, another has patio door and another is entrance to liv room. My speaker positioning is a real compromise. However I found that having full range speakers for the surrounds helps. In our house there is no good way for ceiling or in-wall or even wall-mount. So we had to compromise. It seems to work as it sounds better than before.

And BTW I was told prior to getting into 5.1 that the surrounds aren't all that important as they don't contain all that much information. I beg to differ....at least in my room...and maybe it's because my surrounds are capable...and maybe it's the settings. Dunno. Just sounds good. BTW my surrounds and fronts are KEF 107s (full-range).

I would be most interested to know what other outlaws think of full-range for the surrounds.
HTH