Optimal sub rail thickness for K55 cushions is 1 11/16" with a nose height of 1 27/64". From there you can go up to 1 29/64" to slow the cue ball down, or down to 1 25/64" to speed it up, thats a 1/32nd of an inch swing in up or down in the nose height, but you really need to know what the primary game is being played on the table in order to choose which nose height is best.
I want mine set for 9 ball. Bring your ruler.