Hi Mark,
I put your questions forward to Paul and I have written his response below:
The sole of the plane establishes a certain depth of cut, this can be shallow or heavy, so the depth shoe and the amount the blade is protruding is generally the way we control the amount of wood we remove. The depth shoe can be set for the final depth only, as this is not used to control the shaving thickness of the depth of cut the cutter takes.
Kind Regards,
Izzy