Confused about Spring Collar Height

In testing the new D-Series Prerunner, I found

1. Collar Height affects total spring length, and (if applicable) preload.
2. Spring and Collar height have an unintuitive relationship. The range of maximum front travel settings without preload are approximately

• -0.06m collar height, -0.1m spring height, a difference of 0.040m
• 0.1m collar height, -0.055m spring height, a difference of 0.155m

Some reasonable behaviors of Spring Height and Spring Collar Height would be, either

1. Spring Height as Primary spring length, and Collar Height as jam-nut setting (with a fixed helper-spring length).
Collar Height would not affect total length/preload.

2. Spring Height as Total spring length, and Collar Height as inverse 1:1 changes to the primary spring and secondary length, with a fixed jam-nut position (0 secondary length, probably).
Collar Height would not affect total length/preload.

3. Spring Height as Primary spring length, and Collar Height as Secondary spring length.
Spring Height and Collar Height would have a 1:1 inverse relationship.

Since Collar Height affects total length, 3 is the only remote possibility, but the relationship of Spring and Collar heights are so far from 1:1, any change to one requires fiddling with the other until preload is zero, to know where the preload point is, or to ensure there is none.

Looking for any insights. Thanks.

 

I figured it out..
Spring Height modifies both springs equally
Collar Height adjusts the crossover nut
Collar Height, set to a sufficiently negative value for a given Spring Lenght, can exceed the length of the helper spring, blocking it and making the coilover act as single-rate