It looks like you are standing in your stirrups which is giving you alot of room between your seat and the saddle and could account for being too forward with your upper body. In the 2nd picture, you have lost all contact with your upper leg and only have contact with your calf which also can happen when riders stand in their stirrups instead of just closing your hip angle to get into your jumping position. If your horse is long strided, the standing in the stirrups could result from getting ahead of the horse at the jump. Working on the flat will help to develope universal leg contact from the upper thigh (to stop any knee gripping). Over the fence there should only be a couple inches between your seat and the saddle. As the horse jumps just practice closing your upper body down from the hip. This will clear your seat from the saddle those couple inches and The natural movement over the jump will do the rest. When you "post" yourself over the fence you and get in front of the horses center of gravity, you put yourself in a position that if the horse stops suddenly that you more than likely will go over the front end. Making big moves such as standing into the jumping position will also cause a horse to get faster on the other side.
You've got a good flat back and I like the release, just work on the bottom half as far as not standing and keeping toes in and contact from inner thigh down and you will be a great equitation rider. Oh, I like your horse and you will be amazed at the changes in how the horse jumps as your position gets better.
Just FYI- I am Bntnail's wife not Bntnail. I have not started an account yet but wanted to reply.