Clutch idle position?
 

What regulates the distance of the clutch when in neutral from the flywheel?

Just the pressure created when you depress the peddle. There isn't any type of adjustment on the stock unit. Aftermarket units such as Mcleod street twin do have adjustable masters by which you can adjust how far the travel is.

Are you having an issue? If you feel the clutch isn't fully disengauging you could try bleeding the system, if you have air in it, that could effect the travel.