OK. Will tuning below Fs result in more boomy bass or in more defined LF? How does such tuning sound in subjective terms?
Another way of looking at it that might be helpful for you..
The driver has its own set of physical characteristics. The stiffness of the surround, the stiffness of the spider. The magnetic "grip" of the motor system. The mass of the cone. All these things interact with the air mass trapped behind the driver when mounted in a box to produce a response.
When you put a port in the box it adds another variable. The port is just a small mass of air that resonates at a single frequency. So asking where you tune that frequency in relation to just one parameter and how will it sound is a lot like asking "how fast will my car go with four cylinders?" you need to understand the
system first. See how you go with this:
Thiele / Small parameters explained with real world cases
P.S: There are lots of modelling tools available to help you get a good "alignment" for your driver. Basically, there will be a narrow window of box volume and port tuning that will give you the best compromise for bass extension, transient response and box size. The further you move away from that "alignment" the worse one, or all of those characteristics will be.