Well it appears there is some success with this issue. The Marlin developers have agreed to have both positive and negative values for the Z Probe Offset and will update the LCD to allow +/- offset values. Scroll to the bottom of this issue thread. . https://github.com/MarlinFirmware/Marlin/issues/1682 The changes will be in pull request #1700 - not sure when the changes will be released in a stable version though. More generally it appears to be a good time to engage with the developers and influence what goes into Marlin. So far the Filament Monitor and +/- Z Probe offset are being added. Some good progress is also being made getting the "filament consumed" to be calculated in Marlin and displayed on the LCD.