I watched all your videos and I don't think your position is that bad, but what you really need is much more impulsion. Horses refuse jumps because they don't have enough faith in their rider that they actually want to go over the jump. You have a nice rhythm in your canter, but try stopping the video and looking at little shots of it by dragging the cursor very slowly. See how the canter looks as if it's not going anywhere? That's because his hind legs aren't powering him forward enough.

You want to really get him striding forwards so you can feel him taking you somewhere. The more forward you go, the better the jump will flow. Also, it's much easier for the horse to jump from canter rather than trot, and because you are jumping low fences, you really want the jump to feel like a big canter stride. Really get your leg on to tell Obie you're ready to go!

I wish I'd taken some videos when I was jumping Caddy a few weeks ago, I'm afraid I'm not always the best at explaning what I mean.