During the loading phase the hammer is pushed towards the surface in a controlled movement.
Impact Rebound: At the very end of the movement, the pawl spring releases the hammer mass.
The impact spring contracts causing the hammer mass to strike against the plunger.
A harder roll will reflect more of the impact energy and the rebound distance will increase.
Above all, it is typically the variation in hardness across a given roll that relates most directly to such converting issues with soft edges being perhaps the biggest contributor.