The problem is that the incorrect leg position feels normal to me. When my instructor says my legs are better, I feel like I'm in a chair seat. My stirrups are at the correct length, with the ends hitting just under my ankle with my legs relaxed. Also, one of the A/P Wintec saddles makes it worse, but it's not all the saddle because the dressage saddle doesn't fix it either. It slightly improves, but the majority of the problem is obviously an issue with me.
It's almost like my hips are too supple. My instructor makes a habit of pointing it out to me pretty often, just so I'm aware that I'm doing it. It doesn't seem to be getting better, though. So... Any suggestions?