You are a member over many years I seldom ever disagree with, but this is one.
Leaf spring location relative to the tire contact patch does not change spring rate in ride, as there is not motion ratio other the 1:1.
There is an alteration to the motion ratio based on two possible variables; spring width and track width.
D1= distance of spring width at housing mounting point
D2= distance of track width at contact patch center
Divide D1 by D2 for motion ratio.
For those interested, taking this one step further; square the motion ratio, multiply by spring rate = wheel rate.
Tightening or loosening the dynamics of this can be further altered by splayed mounting of the leafs, ala E body, that will loosen or tighten up a combo but that is getting in to more complex geometrics with the splay, leaf twist, and resulting wheelbase length alterations under compression/extension than I've ever played with.
