I bought a medium tethrd mantis and I've practiced climbing a few times now and I cannot get it right. I think it's fine until I sit or lean back, the bottom that's supposed to go around your butt goes on my butt and the waist loosens all the time(I've put a knot so it won't loosen all the way!). I've tried adjusting the waist, the leg loops, even the micro adjusters and I can't seem to get it right. Should I have gone with a Large? I'm a female that's 5'5 and about 155# somewhat muscular. Or am I just doing something wrong? Maybe my butt/hips are too big? Any advice is appreciated!!!