Yes they are working wheel rate out by squaring MR before they have accounted for spring angle whereas hyper coil are accounting for spring angle for MR and then squaring MR.
So my CPM would come out at 163cpm using that method. If I reduce distance D2 by not using the centre of the tire but the lower ball joint to 15" say I get a cpm of 182cpm!
It certainly doesn't feel like I'm driving a modern day ground effect or downforce racing car! lol
There must be more too this we aren't aware of.