As the two posters before, I have never come across anything on how to touch or grab a control stick or yoke, not in scientific literature nor in pilot training literature. In flight training it all comes down to telling the students not to hold the stick or yoke too firmly. Various references to female body parts have a familiar ring to it. I wonder what references are used when they teach the lady pilots how to hold a control stick.
What I can remember is an article about the Bombardier Challenger 605 in Flight International in 2007 or 2008. The author had flown the aircraft and reported the approximate ratio of aileron, elevator and rudder control forces was something like 2/3/5 (don't quote me on the numbers), a value which had proven fine in aircraft design. Perhaps this and the provisions on control forces in the certification standards might help your search.
If you do a Google Books search for "'ram horn' yoke" you'll find an
article in Flying magazine from May 1985. On page 40 it says:
The most obviously unusual feature is the ram's horn yoke, which is a trademark of British airplanes. The theory behind the shape is that your hand rests more comfortably palm-down on the ram's horn than it does grasping the vertical handle of a conventional control wheel.
I'm afraid this might not be good enough for your purpose, but it shows searching for specific unusual designs could bring you forward. Maybe a further search for articles on the Spitfire's iconic control stick or the side sticks in a Cirrus SR22 will help you.