S is correct. I found exactly the same thing. After a job which took 14 hours, I realised that a density setting of 1 equates to a sideways movement of the bit that is half the diameter of the bit so each pass takes place on a new piece of wood. The bit will keep going over 90% of its previous path if you have the density set to 10 because that density moves the bit sideways at the end of its pass by 0.1mm.