I think he is referring to the location of the control horn on the control surface, relative to the hingeline. Offsetting the horn will decrease the sensitivity in one direction, but will increase it in the opposite direction, which is referred to as differential.
Before computerized radios with aileron differential and individual aileron servos, the horn location was physically offset to provide differential. If you move a control horn on an aileron (or any surface) such that the clevis is aft of the hinge line, you will have positive differential. Alfa models did this on their warbirds that use a single servo cable setup, to provide positive aileron differential.
Positive differential causes the surface to move upward more readily than downward. This is done to reduce adverse yaw effects on ailerons. If you want to reduce the sensitivity, then you will simply move the linkage to a further outward hole in the control horn.