Steps/unit are steps/ unit, and should never change. So, something is wrong.
Are you using a license that came with the machine, or did you buy one in your name?
Homing is controlled by the motion controller, and most do not have an adjustable backoff amount. The UC100 uses the standard Mach3 operation, where it backs off until the switch opens. You can specify this location in Config Homing/Limits, but it won't change the amount it backs off. But, you can edit the homing script to add the back off operation.