about back angle: depends on the disability and user comfortability. adjustable is the ultimate, but if that's not possible a greater open angle is better than tipping forward(many spinal cord injuries paralyze triceps, and it is impossible for that person to push themselves back up if they leaned forward)
about using the chair: ha ha! welcome to my world. it is much smaller and more difficult than yours. You did hit on one of the two advantages to being disabled- good restaurant seating. The other- handicapped parking!
