Why? What does it?
You need to know that just as its importance to have the correct nose height, the body of the cushion must sit at the perfect height behind that nose height in order for the rails to play right. When the rails have thinner subrail thickness, for example 1 1/2" thick, a 1 7/16" nose height is going to be standing the cushion up higher than the backend height of the cushions which will result in the cushions then trapping the balls, making the cushions play dead. The correct cushions for sub-rails 1 1/2" thick is of the K66 design, in which the accufast cushions are, and a nose height of 1 5/16" with a cloth relief on the bottom of the rails to staple the cloth in. Without that cloth relief the nose height needs to be 1 1/4", then the thickness of the cloth will pick up the nose height a little more.