The minimum jump range doesn't take into account the additional fuel weight required by the reserve fuel tank. The smaller jump range is the same value on your statistics screen for your ship.
When you refuel a 16T fuel tank, you get a little extra for the reserve, eg the Diamondback Explorer has a reserve fuel tank of about 0.5T, so in total I get 16.5T of fuel when completely fueled at a station.
Interestingly though I don't think the actual jump itself accounts for that additional weight from the reserve, as I have been able to jump further than what is stated on the statistics screen, so I *think* your actual jump range is the larger "Jump min" figure rather than the smaller one.
FD may of done this so that you can make the maximum jump range specified on your ship, while still having your reserve fuel tank to give you the needed time to collect additional fuel; otherwise you wouldn't even have enough fuel to power your ship long enough to get within fuel scooping range making this "maximum" jump range figure theoretical rather then actual.