My rebounds are just in contact with the hub and can be rotated when the car is at rest on a level surface. This, to me, is the neutral position when the only loading is from the weight of the car. I also think the upper spring should be neutral (or very close) with perhaps just a hint of compression. In this setup when driving, the springs react from neutral to cope with absorbing travel or releasing as the need arises. By having this neutral, just in contact setting there will be no free play that needs to be overcome before the correct effect is met. Balancing spring rates is important, coupled to suitable pitch of the coils. Very simplified I know but it seems a decent base to work from.
I am tempted by the SSL system for the front but would like to try a car with it first.
Fully concur with views on rebounds BUT as far as uppers are concerned, isn’t this trying to defy gravity? They have to carry the weight of the front of the car and no matter how strong the spring, or how long or short, it will always be loaded by that weight, so can never be “neutral” like the rebound springs can be.
Apologies if I have misunderstood?