It must have something to do with the strength of the rail. There the rails we have are 1 21/32'' and subrails 1 5/8'', for a first table, I will glue a 1/8'' hardwood plywood underneath and I will also add 2 bolts per rail , it requires drilling the slates but I will do it. This will certainly add rigidity, eventually we want to modify the metal corners and sides to install pockets that will be flush, currently the pockets protrude above the surface. With this height and this added solidity and a perfect height of the cushion noses we should have a not so bad result I dare believe. What would be the best nose height with 1 3/4'' of subrail, I can install the cushions very precisely this is not a problem for me.