Another couple of days' listening have gone by, and I'm finding the Reso-mat on the bare platter of my tt a bit tonally stark and the sound is less involving and interesting.
To be fair, the platter on the Jap direct drives that I love tend to ring a bit, and do need some damping. The Reso-mat does nothing in the way of platter damping.
So I put the Pioneer's rubber mat on with the Reso-mat on top of that. (And, yes, I always adjusted the VTA accordingly. )
Ah, that's better. Some platter damping with the Reso-mat on top and all is well again.