I didn't notice that. I have them under my preamp chassis. It uses an EI transformer and is very heavy on one corner. I spoke to the manufacturer and he said to place the EVP's so that all three are evenly compressed.
He asked me for a photo and suggested better positioning. So, I have 2 of them close to the transformer and one on the lightweight side of the pre.
I couldn't use traditional positioning but it really sounds great.
My EquiCore is on the floor so I may need to use the foam covered EVP's so that they grip the PC.