Tech tip:

One of the questions that I get asked the most frequently is about the direction of the optional PSS inserts (for ULP/XLP they have part number 308029). Think about it as a upside down V shape, where the wider part goes in first (to the bottom part of the shock body). The idea is for the damping to get (progressively) harder as the piston pushes up.

Source:

A. Hagberg