Yes the factory five link 3.7 Roadster uses stiff rear springs to limit roll which causes an over firm ride given you're close to sitting on the back axle. Adjusting the SSL front damping will make little difference therefore and needs to be several clicks above minimum (about halfway) to control front adequately.
The answer are the dual rate rear coil overs offerered by SSL specifically for the factory five link Roadster Reg. These give an initial soft ride then stiffen up on greater suspension movement to limit roll better than OE. Best of both worlds. They also offer adjustable spring pre-load and adjustable gas assisted damping. I've never needed to adjust the spring pre-load on mine as absolutely no issues, even two up with

's huge suitcase on the back and full tank, from supplied settings as shown below.
![[Linked Image]](https://i.ibb.co/mrb62PC0/IMG-20190911-100740.jpg)