Like Muppet said, drop your ribcage instead of bracing and leaning back. When you get behind your horse like that your horse will kinda "squirt" out in front of you, then you end up in a pulling match trying to stop that energy.
Also your bosal looks too big for your horse, it shouldn't move that far back and touch his jowls, you might want to try a smaller length. When using the bosal you shouldn't pull back and down. Use small lifts to bump him, not pull. The lifts will also encourage him to pick his shoulders up as well.
You guys look good, looks like he wants to stop :)
I DON'T LEAD 'EM AND FEED 'EM, I RIDE 'EM AND SLIDE 'EM.