The fuel flow .v. airspeed curve is the drag.v.airspeed curve ADDED TO the thrust.v. airspeed curve, and the fuel-flow.v.thrust curve.
Because the last two relationships are not uniform (linear) you end up with the bottom of the fuel flow curve not being at the same airspeed at the bottom point on the drag curve. This is basically down to engine / propeller efficiency varying with airspeed and a non-linear power curve.
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