Also the dual spring set up gives a rising rate system. As the main spring reaches maximum compression the lower spring, which has a higher rate, comes into play.
Although I initially thought the same as you it's actually the other way around Peter. Dan at SSL explained as follows:
Both springs compress initially but the shorter spring becomes coil bound first (at around 25mm total compression from static) despite being the higher rate, thus leaving the longer main only in play. Seems counter-intuitive, but when both springs in play, being in series, the combined rate is lower still. Once you've got your head round this it all makes sense
