I think I know....
The bigger the engine is, generally the lower the TSFC, the Thrust Specific Fuel Consumption. TSFC is lbs of fuel of fuel burned, per lb of thrust produced, per hour. IIRC, expect a minimum of .57 for this type of engine. I seem to remember the TSFC was in the range equation, but could be wrong.
What can complicate things here is the TSFC will go up as speed increases (holding pressure altitude etc constant), and contrary to what many may think, it will also go up with pressure altitude (speed etc held constant). IE, you burn more fuel per lb of thrust produces as speed increases, or as altitude increases.