@Jonny5 - Thanks, I'd run across this formula before, and you've confirmed it.

The one aspect that complicates the matter even further, is that the crossover sleeve that sits between the top/bottom sleeves is longer on one end, towards the smaller (primary) spring by default. With that sleeve being longer towards the preload nut, the amount of travel before the secondary rate kicks in is very short - even less as preload increases. This is where I've run into issues in scenarios where I've raised the ride height to the point where the secondary spring rate kicks in with very little dampening.

The tinkering I now have in mind is:
1) Reversing the sleeve to increase the travel on the primary to see if this provides a more lenient path try different combinations.

2) Reversing the sleeve and moving to a stiffer small spring, softer large spring - with the goal being a softer early and mid dampening phase, and a stiff final stage.

I should probably move this to a dedicated topic, but since it was born of Fred's theory I thought I'd at least mention it here with some relevance.