Whatever it does Pnzrldr, it does... sorry, not much help in that regard. We did attempt to get closer to the TMO / RFB handling for the fuel usage several iterations previous, but all we managed to do was "move" the curve. There is no "set" best mileage figure for the boats, and even the mod's included "Maximum range at current speed" function ( <K> key) does not give a true story of what you can attain. In all mods I've tested for comparison, the same holds true for them, in that it changes as you go. You might get a "Current range 9650nm" and expect, using the same speed and other variables that 1000nm later, you would get a "Current range 8650nm", only to instead get maybe 9700nm, or (horrors) 2350nm... We definitely do NOT want the latter occurring, and have "failed" to the safe side of things. But the game does not allow "true" readings for any of that, and does not take into account sea state or currents. We do, however, blame it all on those... lol - We have not changed anything concerning the mileage attained for several iterations of the mod. It is still too "loose" with the efficiency, and we will most likely attempt another run at that, as well as maybe making the boats' bows dig into the waves a pinch more, so that your conn can be "pooped" more often, and let you experienced the taste of sea water better...
To find an approximation of what you can get, the idea is to set your speed and travel for a while (30-60 minutes) at that speed, then ask with the "K" key for what the navigator estimates you can get range-wise. His slide rule is usually off though, so don't expect too much of him... after you get an initial reading, change your speed up or down a knot or two, and repeat the process. You will eventually find the "most efficient" speed of your boat, which should generally be about 9 or 10 knots - but not always. Each boat is slightly different...