I hate to say it, but corner mounting is right up there among the worst things you could do for your sound. The speakers should be about the same distance apart as you are sitting from them, however placement of the speakers is quite critical. Ideally, you want your main speakers about ear level when you are seated. Main speakers generally do want to be pointed more or less directly at the listening area, likely intersecting just a bit behind your head (providing you don't sit right up against the wall). Each speaker setup and room are different, so you'll have to experiment a bit to get it to sound right.