This is probably not the advice you're looking for... but in your other posts you've mentioned
1) you don't know how to half seat
2) you have no real control at the canter
2) your horse rushes jumps
For someone to say that a position is perfect "except the heels" is kind of an oxymoron to me. Heels are such a BIG part of a correct position. It's not just about the heels but not having the heels right means that there are weaknesses in other places which affects your security and thus effectiveness to ride. It all goes together.
Given everything I said above? My biggest advice is to take this time that you have while your trainer is taking off to perfect your basics and work on your foundation. My students starting learning their half seat at their FIRST lesson. At the walk, before they even go into a trot. Before they can canter they must 1) have the correct position and 2) be able to do a posting trot w/no stirrups for an entire lap. Before they can jump they have to be able to steer circles at the canter WITHOUT stirrups. Yes, it takes a long time but basics and foundation are the #1 most important part of riding. Once you have that down jumping will come easily.