I think that a range of 15lyr rather than 12lyr would be more reasonable for ships like the Corvette and FDL. It's not a huge buff, but would make them at least capable of longer trips when bounty hunting or moving from system to system.
The FDL is supposed to be a bounty hunting ship, so I would expect it to have better jump range. Ask yourself, would Boba Fett have put up with a ship that couldn't follow targets between systems?
To balance their low jump distance, a larger class of fuel tank could be considered to upgrade range. Yes, you can buy one for another internal slot now, but for the FDL there isn't the "spare" internal space to use without sacrificing something critical, like fuel scoop or interdictor. The Vulture is in a similar pickle with jump distance and range. A bigger fuel tank would improve matters.
Alternatively, you could always add a longer FSD spin-up time to these ships, so they could jump 25Lyr, but took much longer to jump. After all, if someone started to attack while they were charging, it's not like they're helpless. That gives prey a head start, but no guarantee of easy escape...
Just my view.