Hi PAul,
I think it has something to do with some part of what Steve said.............

Most all of the guys who I have seen fly stunt real good, have quite a bend in their arm at the elbow, close to 90* (definitely NOT "straight armed"). At that position, the hand is basically "vertical". If you straighten out your arm, the hand "tilts" forward.
So, my suggestion, if you are flying pretty "Straight Armed", is to forget that, get a good bend at the elbow and use a "non biased" handle. IMHO, you will become a better "Stunt Pilot".
To "learn" C/L flying, everyone says "fly with your arm straight". "Just raise and lower your arm". That is pretty good for learning to fly a C/L plane around level and not crash, because you are very limited in "control input". But I have not seen that in too many to level stunt pilots, if any.
REMEMBER: this is my opinion, I am sure others will differ. But I do have a lot of acquired "visual" experience to back it up.

Big Bear