Ok. I have tested all night, and found the following:
The backlash calibration procedure:
It is a great idea, however it is kind of cumbersome to use. If you use large step sizes in KSTARS for focus, it is difficult to detect the position at which backlash has ended. Plus atmospheric changes cause small changes in HFR readings to be reliable as a backlash detection method.
I use the graph created when doing an autofocus on K-Stars to look for the position you would expect to see the reverse function go to position and try and come up with a number that makes it stay within the predicted path.
I would recommend using a textbox to allow the user to fill in the backlash value.
The INDI driver moves the focuser to the target position plus the backlash offset. So the final Absolute position is target position +(-) backlash offset. This is not ideal.
I believe this is a limitation of the Esatto not having a proper backlash function.
To work around this the driver should re-sync the absolute position with the backlash offset, and then the driver should go to the target as expected. This scenario should work well.