At the time, I remember questioning Nick's logic about the height of the TR hub vs the MR head not being important. He is obviously a smart and respected bloke, but when you look at the forces involved it seems clear to me there is an effect.
Using a US-direction of rotation helicopter as an example, the source of the two opposing thrust forces that produce the rolling couple are the TR (force to the right as viewed from the rear of the aircraft), and the MR head (leftward component of MR thrust to counterbalance the TR thrust, stopping the aircraft drifting to the right).
If those two forces were applied to the same vertical point, directly opposing one another, there would be no roll, as they wouldn't form a couple. Once they are split vertically, there's a couple and therefore a roll.
The roll continues until the opposing couple (vertical MR thrust balanced by increasing lateral displacement of the C of G from under the rotor head) grows big enough to counterbalance the first-mentioned couple.
The C of G vertical position is important because it affects how quickly that couple will vary with roll angle, but the TR/MR hub lateral displacement from one another is, I believe, equally important.