invTess basically maps user input [0;1] back to [0;1] with a curve that gives more fine control towards the top of the scale. I went back and forth with it and ended up with something like invTess = 1 + 0.2*log(userInput).
I don't set the step size. All control is through chord height, simply because I haven't been able to work out exactly how Creo uses the other parameters. It's adequate for most models.