I think you definitely need to sink down in your heel more, even if you are trying to use your leg-- in both pictures.
I'm not sure if how old your horse is, but he looks hollow in the back. He needs to come over his back and the rock then rocked on to his hind end. Remember: leg to hand, not hand to leg.
I love the other posts about shortening your stirrups! I would do more than a hole, as in the flat work it looks even too long for dressage, and in the photo where you are cantering the knee is below the knee roll, this will also help you sink into your heel and use your calf (which will help him lift his back too).
When you get on stand straight up in your stirrups, and push your weight down thru your heels, then sink in to two point. Hold the two point for at least 20 seconds! You can also try calf raises/heel lifts on the stairs. At the bottom step, stand with the ball of your foot on the ledge and the heel hanging off, drop your heels down below the step then lift them high above to build leg strength, or drop your heels and keep them there for at least 20 seconds to stretch the tendons.
You also look like you have a tendency of sitting behind the vertical, which usually happens when you are driving OR if you are behind the motion. Make sure you sit so that your heels, hips and shoulders are aligned. Tightening the core (and doing crunches or sit ups) will help.
Let me know what you think :)