You should never stack floor mats. Remember the Prius throttle runaway issue which turned into a huge lawsuit and ultimately a recall? The recall fix was to shave off the bottom part of the accelerator pedal because people were stacking floor mats which caused a stuck accelerator pedal. Even though people claimed up and down it was not a floor mat issue, yet after the recall fix, you never heard about another Prius throttle runaway event. People did stupid things and yet Toyota had to pay for it and that expense ultimately gets passed on to consumers.
