If I were to take a guess, I think it is you are changing the geometry (both frt and rear) suspension travel.For example, if you look underneath the rear of your car, at stock height, the control arms angle up toward the center of the car. When you lower it as much as 2 inches, now the control arms are angled up toward the wheel. By doing this, you have changed the arc( or actually the part of the arc it travels in)of the control arms. This in effect changes the distance the arms travel, which will have a small effect on spring rate. Same story on the front.I am not 100% of my idea, but I think someone good at geometry could figure out the difference. And ,just for the record, when we use to lower the rears of 1963 to 82 Corvettes(by installing longer bolts), the cars always road harder.I have been at this stuff a long time, and this is my best explanation.And in the words of Dennis Miller,"I could be wrong".
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My 16th Corvette.
2001 ZO6. Lowered 2 in,04 shocks, HRE 547s, Mich Pilots,Eradispeeds, TPIS,Borla ,Cartek 2X, Blackwing/Power Duct,LS1 Edit,Kirban, DRM Roll Bar,Sparco, Specter Werkes rear facia and C5-R Hdlts, ACI splitter.
515 HP/471 TQ 
CSX1965@comcast.net
