The first thing I can say is hunter`s is meant to look pleasureable, enjoyable and like your mount is the easiest guy in the world. I don`t get that feeling from Jack and I can tell you it`s a direct correlation between all the hardware you have on his face. I can`t tell from the pics on my computer if you`re jumping in draw reins or a running martingale, but either lose them both, now. Despite what your coach may say draw reins are PAINFUL for horses. They force them down onto the bit in a way that pinches their vertibrae, not at all on the bit but a forced image of looking like they are. Go do some research on them and you will be horrified. I assume your problem is his head carriage is too high for hunters. Just from the pictures I can see his also riding completely off of your hands, which looks really uncomfortable for you. This is completely because Jack is looking for some relief from the hardware and using your hands as a crutch to lessen the effect of them. Before you go around jumping with all the hardware and big bits, stop and do some simple flat work and relaxation work with your horse. Get a dressage coach out there and learn to bring your down using your riding ability, not some leather tack. I can guarantee he will resist you less and rip your hands off less. Nothing works like sitting back, driving, and a gentle hand. No good is coming from all the hardware, only hardening his mouth and making it easier and easier for jack to evade you. If you worked on that, I could see a beautiful hunter pair taking home ribbons.
If something is not to your liking, change your liking- the only thing you can count on in this world is change. ♥