Yes I agree, you are right.
On my Plus 4, when the car is jacked, the upper spring compress fully the rebound spring. If you cut the rebound spring it implies that in rebound position as you said the stiffness of both springs are added and in this case you could get a stiffer system with less rebound travel when a rebond occurs.
But when the suspension is in normal position or compression with a free rebound spring you get only the stiffness of the upper spring.
The choice of a shorter rebound spring with less stiffness perhaps could seem more appropriate.
I guess that Suplex is a smart answer to solve this problem.
