Wholesome creamy goodness
HKS GT4 owner here...yes, the HKS coilovers have a small rubber "spacer" between the spring and top perch.
After reading all available info i can find on coilovers in general it seems that the harshness comes from the top mounts and getting rid of the rubber for a solid mount.
kw's keep the stock rubber top mounts. In some of the pictures of the HKS IV looks as if they have a rubber peace in the center of the solid top mount which should help or stop harshness also
but the info sheet is in Japanese so i cant say for sure what its purpose actually is? would be helpful to know what it says in english.