The amount of pigmentation is 100% random, low white parents can produce high white offspring and vise versa and there is no predictability in it. However, there are some codominant/incomplete dominant genes that can affect pied coloration in ways that are very predictable; ex. Lesser/butter pieds are all white (same for champagne pieds), spider pieds are always extremely high white (some completely white), cinnamon/black pastel pieds tend to be very high white, and enchi pieds are almost always low white.
To my knowledge there are no recessive genes that affect pied in this manner.