It has an Fs of 41.9... why cant it be tuned at 45hz?
You are new to this and you have a little trouble getting the hang of it.
First that driver is very sensitive. There is an inviolable inverse relationship between bass extension and sensitivity/efficiency of a driver.
The other issue is the stiffness of the suspension. If you have a stiff spring it will oscillate faster.
Now Emminence who make that driver are primarily instrument speaker manufacturers. For that sensitivity is king and not bass extension. So that driver is right in line with their history.
The only way you could extend the bass would be to build an enormous back loaded horn. That driver would be a really good driver for a horn design given the T/S parameters.
However if you look at the design I did for you, this drivers does work for an extended bass alignment. The box Fb is actually 38.7 Hz. The bass roll off is relatively shallow from F3 to 45 Hz where it is only 6 db down. So you are not really arguing over anything important. The key is that the cabinet design is properly done for the driver in question and this design achieves that.