[YodasLuke]

Can we change a word in the question from OR to AND, so I can respond? I like to have options...as Mr. Kelley intended.

Homer did give recommendations, which I will follow. But, in the end, he wanted you to pick something that stayed still. If you use the head, your eyes can see more under the ball if the head moves, giving visual feedback. Thus, 2-0-A-#1 does not say a stationary neck.

There's a minimal difference in using either application, but the base of the neck allows the eyes to move. If they move, how much is too much? When does it become a sway? How can your eyes warn you upon achieving too much movement? Is it at 2.7 or 2.8 centimeters? Your guess is as good as mine.

Just keep something still so the left shoulder (center) has an additional center around which to operate, and you'll be better for it. Is that too difficult?