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You could try
Backlash 100 (or more. (More is ok, less is not)
Steo size 30 (for e 3 to 4 times minimum HFD)
Number of steps: 9 (7 to 9 are recommended)
And see if the roll-off disapears
If you are focusing “IN” then when the focuser goes “OUT” to start the focusing process it will move an amount depending on your number of steps and the step size plus the backlash amount, in the OUT direction, and then inmediatelly will move”IN” the same backlash amount to take care of the backlash and start getting the data for the first point to the right side of the focusing “V” curve.
But the best you could do is to try focusing with a larger backlash setting, 100 or more, and see what happens. More is OK, it will not affect your focusing, less is a no-no, it will affect focusing.