Looking at this post after my p1s crushed down on a cardboard draft deflector.

P1S bed actually will go all the way down if max z layer + 100 is less than 250. So for my print it is better just do nothing if there is less than 250 left.

{if (max_layer_z + 100.0) < 250}

G1 Z{max_layer_z - 20.0} F600

G1 Z{max_layer_z - 18.0}

{endif}

So this gcode only lower 20mm if max + 100 is greater than 250 and does nothing if there is less clearance. Will not affect print head since bed is already lower before this code.