Let me clarify this up for you. With some suspensions such as the RE MT, the spider materials fatigue causing a lower score...SPL wise. Also, with a tighter suspension would generally mean a higher FS, hence contributing with the resonance of the vehicle and attain the louder number. Once, the suspension has broken in, the FS typically drops and allows the woofer to play better lower frequencies. The trade off is SPL in terms of vehicle resonance.
One the other hand, companies such as Digital Designs uses a higher grade spider that does not fatigue. In this case, the subwoofer will be louder with more excursion as it is being broken in.
Let me know if that clarifies it. If not, ask more questions.
Tuan