Changing Distance Driver Object Must Move for the Shape Key to Change.

So I have a Driver assigned to my one of my shape keys, the object that changes the Shape Key’s Value is an empty. Currently I have it set up so that if the empty moves 1 blender unit in the Z direction, the Shape Key will go from 0 to 1.
I would like to change it so that it only has to move 0.5 blender units for the Shape Key to go from 0 to 1.

information about driver:

Been meaning to do a video tut about the graph editor and drivers, since it seems most people don’t understand how it works. Here’s a quickie:

In the graph editor for drivers, the x-axis (horizontal) is the input of the driver. The y-axis (vertical) is the output of the driver. The output is the value shown in your screenshots when debug info is checked, and it’s also the value sent to what’s driven. The input, in your case is the z location of an empty, right? Your generator modifier settings should produce a 1 to 1 curve, as the empty is moved. So if you change the curve to be a .5 to 1 curve, that is at x = .5, y = 1 the line passes thru that point (minus the offset you have, the value in y = -10.00). So if you change the value in front of x in that expression to a 2, it should give you a .5 to 1 curve.