on stomach?

This position is fine. I do think it stimulates my penis more but I have achieved super-O's in this position. You can lie flat or put a pillow under your hips. What I like about this position is spreading my legs about 30-45 degrees this gives me a freedom of movement with the aneros inserted. The handle can not touch any part of my gluteus muscle. Sometimes I pull my knees up under my pelvis it still feels very good and you can not get into any more of a receptive position than this. Depending on the how high your bed is B. Mayfield has suggested kneeling beside or bending over the bed. Both are good position to stimulate your prostate gland.