Hotchkiss Leafs Installed

I agree the torsion bar is not progressive, so I am not assuming the rate will change. However, once lowered the t bar is completely unloaded, kind of like a coil spring that would be completely unloaded at ride height - not a good thing.
Another thing is the bumpsteer on E bodies is MUCH greater than with A bodies. I have not checked mine yet, but, the tests Bill Reilly did many years ago showed the bump steer through the entire range and it was pretty minimal.
The third thing here is the roll center is raised, but when the roll center is below ground with the current setup, its what you want. This is why the car feels better. Put all the proper angles together with good tires and alignment, and you have something that works well.