If you look at the horse you are riding, it has a very round barrel. It would be very hard for any human to postition their leg so that it draped down , wiht the kneecap facing forward, and the toes pointing forward, especially any FEMALE human being.
We females have a bit more difficulty NOT having our knee roll outward just due to our pelvis shape. But that pony is so wide that he pushes you knees out, and thus they tend to roll outward, and thus your whole lower leg rolls outward; all to accomodate the round barrel.
Do you have similar issues on a narrower horse?