I am about to mount my rear surrounds on a back wall. My question is the width dispersion. I have them currently set-up 6' high and the separation is about 11' from each other. Each speaker is about 6'' off of each side of the couch. My question is there a maximum width for the rear surrounds, and is 11' too far apart?? My side surrounds have to be mounted in the ceiling as well. FYI these are in wall speakers.

Search out a setup diagram, perhaps at the Dolby Labs or THX websites. They are normally expressed as degrees off the listening area, so it would depend upon how far behind you the speakers are located.

11 ft might be too far apart. Kinda depends on the room width. You want to have a good amount of distance between the back and side surrounds.
Some sites (dts, DD, THX) show the back surrounds side/side. Others show about 6~8ft.

I personally have my back speakers spread about 9 ft, as I have an 8'-8" wide archway in the back wall. The room is 17.5 ft wide with the side surrounds wall mounted, so that gives me about 7 ft distance from RB~RS, LB~LS.

I checked the Dolby diagram and they do state degrees but nothing about width so I am assuming this does not matter? The speakers are about 5' behind me. Room dimensions are 16'x19'

I checked the Dolby diagram and they do state degrees but nothing about width so I am assuming this does not matter? The speakers are about 5' behind me.If you spread your rear speakers too far apart, then they won't be able to anchor sounds behind you and won't be well separated from the side speakers. Place them too close together, and you won't be able to hear left-vs-right stereo separation behind you.

My layout is similar to the Dolby diagram, with the rear speakers spread roughly 60 degrees apart. The easy way to figure it out is to measure from the sweet spot to the back wall and multiply by 1.2 to get the rear speaker spread. So, if the back wall is 5 feet behind you, then the rear speakers should be at least 6 feet apart (5 x 1.2 = 6). And you'll have a 60 degree spread.