When setting up support structure for a Stylus to perform at its optimised / close to optimised. My experiences had, has discovered that 2mm (1/16) in a thickness of a materials used under the Stylus can make a major difference.
The TT is not up and running at present, but because I was very impressed by the AT 677 Mat, I have a Micro Seiki Copy of a Mat made in very similar metal to the AT 677, but at a 10mm, approx' (3/8) thickness.
Forex Foam Mats used as 5mm Thick Mat, are in my set up extremely attractive in use on both ID TT and DD TT's. Take the same material mat in less than 5mm, when used in my system on a DD TT, the outcome is the usage is very short lived. This material type at lesser thicknesses does not perform attractively.
The same outcome occurred on a system in another Home on a BD TT, the system owner was so impressed with the 5mm Mat I gifted it to them.