Tightening pockets effectively shallows shelf?

Below is an excerpt from the BCA pocket specs for the pocket shelves. As for the corner pockets I would say most definitely that you are not going to be able to extend the sub rails without shortening the distance from the imaginary line to the center of the slate vertical cut. I suppose that's why they allow a plus or minus of 1/4".

For the side pockets that distance will not change, no matter how much you tighten the pockets.

I read on the forum somewhere that Diamond has special cut slates to allow for the deep shelf with tight pockets. I think RKC (aka Glen) mentioned that. As for how much it changes, I just measured one of my corner pockets at 4-3/4" and if I have the subrails extended to a pro-cut size of 4-1/2" pockets it will reduce the shelf roughly by 3/16". Hope this helps.

BCA Excerpt
Shelf: The shelf is measured from the center of the imaginary line that goes from one side of the mouth to the other where the nose of the cushion changes direction to the center of the vertical cut of the slate pocket radius.

Corner Pocket........................................1 5/8" minimum to 1 7/8" maximum

Side Pocket............................................0" minimum to 3/8" maximum