Bass Robbing Mats!

I could be mistaken here but IIRC felt mats were largely an instigation of one manufacturer producing a TT often noted to have a "bass bloom" and another using a glass platter with a tendency to "ring".

Virtually all the DD and idler drive manufacturers seem to have used rubber, although economics, durability and a need to dampen the "ringing" of metal platters will also have played a part.

I have seen recommendations of a cork/neoprene gasket material being made also.

That said, my own trials of a number of mats and combinations indicated a tendency for them to affect the sound rather as one would expect from their various materials.

I have also noted that the record/platter interface is part of an entire resonant system that includes the TT feet, support stand, cartridge/arm, arm/plinth and even (for MC) the cartridge loading.

Changes to any of these interfaces can affect the effects of other parts of the system, eg some mats will sound good used with one support system but not so with another.

Much opportunity for tweaking here 

Does your experience of that mat bear out those claims ?  Have you compared it to any other materials/mats ?

IIRC you have been having issues with over brightness - IME harder materials will often have a "harder" (and more detailed/defined) and brighter sound than softer, more resilient ones.

Perhaps some mat experimentation is in order.

Many materials have been tried to good effect on different tables/platters at different times and include vinyl, special composition (Funk Achromat), graphite, leather, lead, various foams, silicone, patent treated steel sheet (SDS), cork, bitumen sheet and of course felt and basic black (rubber) - I rather like the characteristics of the funk on the 2 tables I have tried it on, on an acrylic platter on one and over a 2mm silicone mat on an alloy platter on the other.