My planer isn’t adjustable. I’m guessing it removes 1/16th inch or more off the soap. I rarely need to remove that much, so I put paper under the soap to raise it up until the layer of soap removed is more like 1/32 of an inch or less. How much to plane off will depend on how bumpy the soap is. I would rather make two passes to take off very thin layers rather then one pass that takes off too much.