Everything on this thread has been great advice, but I would just add one more thing to consider. It may or may not be true for you. You say that you know you ride defensively, and also that your horse really uses himself over fences - do you consider your horse quite forward? A lot of riders begin riding defensively when their horse is a bit out of their comfort zone (for any reason - too exuberant over jumps, too hot, huge stride, or known behavioral issues). The inclination for the rider is to lengthen stirrups a hole or two, shorten the reins, and start sitting up early. Of course, this is exactly the opposite of what we “should” do! That’s not a comment on the rider’s ability, it’s just a subconscious defense mechanism of the body trying to protect itself.
If you have any notion that this might be you, you can start by looking at your leg. Chances are your stirrups are too long, and shortening them will give you a better base of support. The “ankle bone” measure isn’t universal. Now with your stirrups at the correct length, does your saddle still fit or is your knee trying to inch past the flap, or is the stirrup bar too far forward/back? You should be able to hold two-point at the trot with ease (your leg staying stable - not you fighting for it or trying to force your leg in the correct position).
Then, get comfortable with letting your horse move out. That doesn’t mean flat out galloping with a death grip, it means holding your two point without balancing on the reins and allowing the horse to use himself fully. If you’re not comfortable with a forward canter on a loose rein, that might be some of your problem (not saying this is you - I just see this surprisingly often!). If that’s fine, are you comfortable holding your position and letting your horse pop through a simple in and out at a forward pace? How about a whole course? If there is a confidence piece to work on, you may find hesitation in one of the above exercises. If you have a legitimate reason to ride defensively (rushing/bolting etc) ensure you’re doing an exercise that is appropriate for you. However, as you already know, the defensiveness makes all of the above worse, so building your confidence by having a strong base of support and knowing you can stay with your mount will help both of you relax and stay in sync.