Rhyno,
The biggest factor is speed. The speed determines how quickly the swept volume or the displaced fluid must travel through the psiton and shim stack. The more the volume of fluid for given time the greater the deflection required, and inversly true all things being equal. Most current good suspension companies use a mix of calculations, SWAG, and exsperience to determine this realtionship. Interestinly enough the total deflections for the diferent systems wether high or low flow seem to be very simmilar as the given area of the varibale orfice becomes almost exponetial in nature, as deflection increaes. The real trick seems to be controling lower defelections.
Regards,
Jer