It can, but you (the rider) have more to do with that the fin itself. If you push the fin all the way up in the fin box it'll loosen it up, if you pull it closer to the tail it'll stiffen up. The more loose it is the sharper turns you can pull but the stiffer you go the harder it is to turn and it'll force a straighter line, however it is more stable. All depends on what you're going for.
Yes. Keep in mind that when you do a turn on a thruster, your inside rail fin does the heavy lifting... that's the fin that provides the "pivot," (although that's a bad word to use) and the majority of hold. The trailing fin adds directional control, stability, and drive, meaning how much speed and projection you carry through turns. It also has a "centering" effect when going from rail-to-rail. Increasing the size of your center fin will increase all of these attributes.
