Make sure you wait and let your horse thrust you into two point when jumping- you are anticipating and jumping before your horse. You can't know when or where your horse will take off, you have to wait and let the horse jump under you and put you into position. I had a terrible time with doing that until recently, it takes a lot of practice.
A note about the horse... has a vet done any x-rays on your horse's knees and back that showed they are all fused together? By 4 years old, 90% of horses are still developing their back and knees, they usually don't fuse together until 5 or 6, rarely later or earlier. IMO, at 4 years old, horses are just starting to get mental maturity and they should start working on dressage - every jumping horse should have basic dressage as their base. Until Cowboy is 5 or 6, I would not go over the height you are jumping right now, and do it very lightly (every week or two).
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown