Is this a normal sex position? do other people do this regularly?

After having sex in all the usual ways for some time, my GF now only prefers one position. She mounts me cowgirl style and then lays flat on top of me and moves both legs to the inside so that my legs are now spread for her. We are in Missionary position exactly but reversed roles. She comes repeatedly and VERY easily this way. I've played around a bit and figured out how to get my legs around her bum which drives her over the edge every time. She grasps me tightly so I can't reach her breasts and has gotten pretty good at keeping a rhythm going. It's a great orgasm but I do feel a little dominated (new feeling - not bad I suppose). kinda funny since I'm a foot taller than her. What is the name of this position?