Actually, this weekend at our contest, I noticed that about 1/3rd of the "Expert" flyers laid their hand over to horizontal during the inverted flight portion (palm up). During maneuvers, most tend to follow the plane with the hand also but that masks the actual direction they are pointing the handle. Very few keep the handle vertical at all times.

I have consciously tried to keep my hand vertical at least during the inverted flight portion, but I end up having to concentrate on the handle instead of the plane, and the actual flight sucks so now I just figure that my hand belongs wherever my brain subconsciously tries to put it and my attention belongs on the plane.