The size of the horse I am getting training on is very small, not a pony, but it's very small, her slow trot is very smooth, i find myself rising high and down, but the saddle is deep enough, so i can follow the movement by staying deep in it, but when I try to increase the trot speed, i can't follow the high ups and downs, and i almost hear the sound of my seat hitting the saddle, not much, but not too smooth as well, is this normal? or i am missing something?

By the way, you answers reflect clear understanding i see thanks alot