-Your legs are in front of you. You should be able to draw a straight line through your hip and your heel. Bring your legs back so that your toe is on the girth
-It looks like you could leghten your stirrups. You don't need them that high for jumping those heights. This way you will sink further down into the center of the saddle
-When you release you need to move your hands up the neck. And close your fingers more so that you have total control of the reins.
Overall you have a very nice center of balance. And you seem to be able to feel the horses take off very well. You have a nice foundation and a natural back.