Problem with some positions because of height difference.

Hey guys. Me and my girlfriend (M20, F20) have a bit of a problem with some positions. I'm 200cm tall (6'7) and my gf is 170cm tall (5'7). We have a problem with position where I'm on top. For example missionary. I'm too tall and I can barely reach her vagina. It's really uncomfortable. Can you recommend some positions for people with big height difference. Especially ones that the guy is on top.