As noted from the ecomodder link above (actually using my image without attribution to me or especially the original source, even quoting my words verbatim without attribution), the BSFC is not one specific value but changes throughout the engine load/speed range.
It is true that in almost all vehicular applications, the best-point BSFC is not really anywhere near where one predominantly drives - this is where hybrid drivetrains derive some of its economy advantages.
The best one can do is operate - as much as possible - at the range of lowest BSFC for given driving speeds and conditions and, with very few exceptions noted, this almost always occurs when driving at the highest gear without severely lugging the engine.