In some cases I think we have the blind leading the blind here, and I count myself among the blind because I'm neither a mechanic nor a performance tuner. However, my understanding is that adjusting the ride height with coilovers has to do with pre-tensioning the springs with the double-nut mechanism, which does nothing but ride on the outside of the shock tube. The damping/rebound is adjusted via the internal shock valving linked to an external knob. Two different functions. Max firm does not equal max lowering. Coilovers typically offer adjustable drop of 0" to 2" below stock ride height. The spring-only kits for Boxster generally have a fixed ride height of about 1" lower than stock. Of course it's never exactly the same on two different cars or even two "identical" springs on the same car.
