That documentation is helping you to get the step size, Let's say that your infocus position is 5000 and your out of focus position (approximately 3x HFR over your best HFR) is 7000 and that you want to use 7 total samples:
(7000 - 5000) * 2 / (7 - 1) = 666.66666 steps per sample, or 670 steps.
So rather than defining the step size you should calculate that based on the number of samples you want to acquire. 7 or 9 is generally a good range, but keep it odd.
Hope that helps.