On the subject of the hands. Don't pay too much attention to what I am about to say, I'm only brainstorming, and with JPs there are so many things affecting other things, that improving one thing often makes others worse. That said, it seems to me that if the origin of the hand is aligned to point straight down the middle of the forearm (and parallel with the with the palm), the scope of the twist can be extended from near the wrist to the elbow, without too much distortion of the forearm. It's just a thought for your consideration.

P.S. deleted a previous post, because the values I gave were rubbish.