Shorten your reins. That'll bring your hands out in front of his withers, rather than behind your pommel. It will also give you a better feel of his mouth.
I'd also think about dropping your stirrups a hole - in a couple of the pics, they look really short, and in the others they look okay, but I think you'll have an easier time if they're a little longer. It also looks like you put most of your weight on your toe - I see that you do some bareback riding already, which is great. Start doing some of your schooling bareback, or stirrupless, to help you be less dependent on your stirrup.
Your posture is very nice and relaxed - good job! That's something I struggle with...I'm like the Hunchback of Notre Dame when I ride.

Anyway, I think once you've fixed your leg position you'll be much more effective, and you also won't be tempted to throw yourself in front of the saddle at the posting trot, as you are in the last picture. It'll be an easy fix if you put the time into correcting it!
