All three brushes sit on "ramped" adjustments that allow them to be slid up and down along the ramp's length -- which in turn moves the bristles in and out. This allows the user to adjust the bristles so that all three equally and uniformly contact the arrow shaft at the same time.

If the two on top didn't contact at the same time, it would allow leeway for "wobble" as the shaft shot out of the rest; by having them contact all at once, you get the benefit of the Whisker Biscuit's "full containment" theory, but in a much more highly adjustable platform -- and without the disadvantages of the fletching contact.