There is no gap between the arm and the stop bolt when the slave cylinder to arm spring is in place. The gap is set (with the slave to arm spring off) by holding the arm all the way back and setting the gap by changing the stop bolt's "length."
The arm does not move towards the flywheel housing as the clutch wears. It can only go as far as the stop bolt which is were it is with the slave spring in place.
What the gap setting is doing is placing the throw out bearing a correct distance from the inner clutch spring. In effect it is placing the clutch pedal in the correct position when the clutch is released to shift gears.
Decreasing the gap means the pedal reacts lower, and visa versa.

My clutch is working fine—just thought I’d check the return stop adjustment. Haynes sez .50mm between the clutch arm and the stop bolt. OK, but I cannot understand why it would matter… 5mm or 500mm as long as the travel of the arm isn’t restricted by the stop bolt. As the clutch wears the arm moves toward the flywheel housing, right? Yet for some reason were supposed to keep the stop bolt away from the arm by .50mm? What difference does it make when the arm never touches the stop bolt (w/ clutch fully engaged, peddle out) in the first place? If fact, why have a stop bolt at all. Also, Haynes sez to remove the return spring when measuring the gap. Besides being a PIA to remove, the clutch arm is kept from moving by the clutch slave cylinder, spring or no spring. What am I missing here?