Pretty much everyone with a semi-circular shooter either emulated, or ended up with something similar to 973's design. Ours was a 60 degree arc (arc radius = diameter of frisbee + radius of shooter wheel) minus a small amount to add some compression to the frisbee.
This image shows their shooter pretty well.
http://www.greybots.com/uploads/1/4/...0_orig.jpg?292
This was shown to be one of the most effective designs by the time the season had ended. I would highly recommend starting with that and changing as necessary.