Here’s the way it works, hopefully I don’t miss anything:
If you set focus, it will lock out the material height field
If you enter a material thickness, it will still auto scan to set the material thickness at the beginning of the job because the most accurate measurement for focus is the distance from the head to the material, not material thickness.
If focus height = material thickness, it will always use the auto focus measurement.
If the autofocus measurement fails for some reason, it will fall back to the material thickness field.
If the focus height is different from the material thickness field, it will respect the focus height field in setting focus, but it will still scan the material beforehand to take the measurement.