The rubber is not needed. The perches have a spring built into them and once there is load on the perch from the weight of the car being applied on the entire suspension there is no movement.
This never was about the thickness of the rubber having an effect on ride height. It was more how the rubber fit on the new perch and the fact that its not needed.
If properly installed there are no squeeks or pops at all.
If you would like to install the rubber perch you can. We just dont recommend it.