I can relate. I have a pretty good position at a walk, but it aint so great after that.
one thing that can help, as an alternate image to kneeling, is to think of the bottom of your feet as being pushed down toward the ground, BUT, they must be parallel to the ground. and you aren't pushing the ground, but kind of imagine them being low toward it and just skimming over the ground, parallel to it. yes, my leg gets longer, but it's kind of down and back orientation as I focus the heel toward the horse's back feet, and imagine my foot just skimming over the ground.