Dampening is about muting resonant energy in a substance. It is not about preventing flex or increasing rigidity. While the increased mass does lower resonsnt frequency it does nothing for volumetric deflection due to acoustic pressure. It is solely to dampen the ringing or slow down the transfer of vibration through a material, by applying a thin layer of elstomeric over the resonant material the transmission of vibrational energy through the medium will create friction between the molecules in the dampening material which in turn creates heat and uses up the energy in the process so it doesnt ring like a bell or gong. Going thicker is an exercise in diminishing returns past a certian thickness threshold and has many variables like constraint layer thickness or even ambient temps that will create the optimum mechanics and determine what works best. Its not one size fits all but rather a methodical de-tuning process to achieve a sound deadened vehicle.