In a 5.1 setup, is the ideal placement of left/right surround speakers suppose to be on the side walls or on the back wall angled towards the listening position?
Either way and whatever works best physically.
Just wanted to know if my seats are 1-2 feet away from the back wall, will it be okay to place the left/right surround speakers on the back wall and angle them towards the seating position?
Unfortunately, if you're going to be that close to the surrounds, small lateral movements of the listeners head can easily create huge shifts in the surround field.
Looking at Dolby's Web site, they recommend a 90-110 degree angle for the left/right surround speakers in a 5.1 setup. I guess a 110 degree angle means it is acceptable to place them just behind the seating position but angled towards the seating position?
In 5.1, I'd suggest striving for 110°, or as close as you can get to this. It's ok to be off from the angular position, just try to get it close.
To help matters, I've had great luck elevating the surrounds up to ceiling height, aiming them down and in directly at the primary LP. I'd say getting them further away from the listeners head, is more important than maintaining them at a specific height. Point being, don't forget about the ceiling.
I've recently changed my surrounds to a rail system, up on my ceiling, whereby I can re-located any of my four surrounds relatively easily. They can move as a group of two, or individually. I'm 7.x, with sides a bit forward of the LP, and rears about 20° back. They're yoke mounted, so I can aim them in any direction, place them anywhere in a ~10' square.
I hope this is helpful.