The more I think about it, that might work.

I don't really understand the Home Off and Back Off issue that you guys are discussing but can tell you that I use my  home mech. switch/opto sensor combo as the master tool 0 located at X0.  All 14 of my "real" tools are set up referenced from that point and its been working very well.  I use a microswitch to close the circuit to the opto home sensor which is referenced on the edge of a slotted disc on t'other end of the X-axis double shaft stepper motor.  Poor man's servo index pulse like my hero Hood uses.  I use the PP and dunno if it works the same with an ESS?

DB, Home off and back off are 2 different terms

"Home off", or offset within Mach is intended for you to set a specific value. Upon reaching the switch, the DRO shows that value. It can be either end of the travel. My switch for example in machine coordinates should be the most X+  and X0 should be the center of the spindle. Using Mach3 and a PP I can achieve that. If I wanted it the opposite, I could do that too. Whichever way you can fathom it, you could set it up that way.

"Back off" which is a setting within the ESS configuration is the physical amount you want the machine to travel in the opposite direction after the state of a limit switch is triggered. This would get the machine off of a limit or home switch instead of mandating a limit override request.

For some reason using the combination of ESS and Mach seems to have a conflict or produce some weird actions.

If I put 0 in the home off of Mach but .1 in the back off off the ESS. The machine will upon triggering the limit/home switch will back off the value inserted (.1 in this case) it will show this value in the DRO. If using Mach alone it would show whatever was in the home off value (0) machine coordinate.

Lets say I would like the DRO to be 6" since the X axis is at its largest + value. If I put 6 in the home offset box instead of that value being shown in the DRO, the machine moves off of the switch 6". Regardless of the value in the ESS back off configuration.