For those of you struggling with your leg position. This is the exercise I have my students do for homework.
Start by doing true to form squats going up and down while holding your core tight and upper body straight. This will help train your muscles.
Next get on a yoga ball, hover your seat above it just slightly, leg back under so you are lined shoulder, hip, heel and do slight pelvic tilts.
The biggest mistake people make is actually rising in their rising trot. Its not a rise, its just a slight pelvic tilt(refer to video I posted earlier)
Now when you get on your horse after you do your warm up, drop your stirrups. I will completely remove the stirrups off my students saddles and for an entire month we do no stirrup work practicing rising trot. Believe it or not, once you do it no stirrups you will realize just how much you are over rising when you have your stirrups. Its just a slight forward and back movement with your hips, using your thighs to "rise".
If I remember I will do video this week for an example if you would like