Sorbathane under granite slabs for speaker bases?

I’m getting two 12"x12" granite slabs to use as bases under my KEF Reference Model 2s via spikes. They will be sitting on a 5" high hollow tile shelf. Would using thin (.25") 70 duro sorbathane under the slabs help in isolating the speakers or will it possibly negatively impact the sound?

Thanks for any input.