The thing is, it does sound like a leveling spring.
Given the same vehicle and payload, a heavier spring rate will affect travel in both compression and extension since higher loads (on the spring) are required to extend/compress them. This is evidenced by your comment on less body roll.
I am very interested to see how these develop, and I hope they publish spring data (rates, lengths, number of coils, etc.). Lengthening the spring vs. adding coils could be a step in the right direction, but full spring data is needed.