Just curious... do you have a Track Pack car, or aftermarket dampers? If so, was you car corner balanced for a single driver, or driver & passenger?I am also dubious about the 'added weight= less grip' axiom both these articles are predicated on. For one thing, the Lotus exhibits more tenacious grip (most notably in slow turns) when I have passenger onboard. Also, aerodynamic downforce increases grip. It may be that the force vector has a lot do with how the contact patch responds.
If you don't have an adjustable suspension, it just might be that the car is better corner balanced with a passenger on board... (not to mention the fact that you'll get less body roll on right hand turns with a passenger)
EDIT: Also, aero downforce increases the downward force vector on the tires without increasing mass... that's why it works...