I had a 12.1hh pony that would probably have easily been able to clear his height and more - he could jump 3' from a trot, and a really crappy one lacking in impulsion at that (not my crappy riding so much as his sheer laziness - it was all you could do to GET a trot). He was REALLY bold too, so long as the striding was ok he would try.
My 15.1hh Anglo jumped 4' within the last 12 or 18 months (can't remember which) and he will be considered 16 in august. I think, had he been given the training at a younger age, he could well be capable of doing courses at that height and higher. Single jumps like in puissance, I don't even know. He is a horse with enormous heart and athleticism. He was evented consistently, at a medium-high level (I don't know what it's called in America, but here it's called prelim/B grade) from 4yo to 10yo and then ruined by crap riding, left in a paddock for 4 years, and eventually rescued. I bought him from his rescuer. I have had a few people tell me they remember him from his younger days. He is the horse that has that 'x-factor' that makes the difference between a C-grader and a B- to A-grader. Could he jump more than his own height? Frankly, I've no idea. He is considered 'small' for a showjumper as here they tend to be 16hh+.