By looking at the pictures it seems as though you are pinching with your thighs and knees over the jumps. This causes your lower leg to slip back and your heel to come up which is what's happening to you. To fix it, you can obviously do lots of two-point in your groundwork, but really concentrate on opening up your thighs at your hip and also point your toe slightly outward to keep your knees from pinching. By fixing the problem of pinching it will also correct your upper body to not be quite as forward...it probably won't be a drastic change in your upper body, but it definitely be a noticeable one.
If you work on that in the flat you might also feel your horse's shoulder move a little more freely because pinching your knee restricts the movement in the horse's shoulder.
While Riding A Horse, We Borrow Freedom