OK Syd, a genuine question for my education:
We have been discussing couples that create rotation of a body - how do you identify the axis of that rotation? Is it along the line between (in this case as in ACs diagram) MR head and TR and, if so, where along that line?
My point about height of TR having little effect is that I have flown helicopters with both high and low TR (of both clockwise and anti-clockwise rotation and differing head designs) yet the roll angle in the hover is always between 2 and 4 degrees with that upper limit being on a semi rigid MRH with a large effective hinge offset.