surround sound speaker fine tuning

[PoorSignal]

My rear speakers are up there on a shelf about 4 feet above my head. I had always aimed them a bit forward. Now I am trying to have it shooting straight at each other, parallel with the backwall like the diagram in the Dolby publications.

Wouldn't the phase cancel out big time doing this leaving me with a hallow anemic bass?

Next, when putting the speakers sideways, is too close to the backwall a bad thing? the woofer is about 4" from the back wall. I think the sound might be better if put more forward, even more forward than my head than the sound bouncing off the backwall.