What I am trying to describe is changing the amount of derailer movement that a certain amount of cable pull causes. The photos show the extreme example, to get an 8sp shifter to work with 9sp gears or vice versa. Basically what that accomplishes, is to change the amount of derailer pull for each click in the shifter.
Ok, I think I understand now--the position of the cable on the pinch bolt affects the distance the derailleur moves when shifting.
I'm not sure this explains the noises on the high gear though--with no cable tension (shift cable unbolted), and just by moving the guide cog with the H screw, there's no position achievable where the noise goes away...