Who is BS'ing who?

OK lets talk about operating efficiency at different RPM ranges (for the sake of this discussion we must assume an engine in good working order and properly tuned)
efficiency being defined as the amount of fuel needed to cause the engine to turn one revolution
yes it is true that an engine can run more efficiently at a higher RPM, meaning that it takes less fuel to turn one revolution than at another or lower RPM range, and that does have some effect on fuel mileage
that doesn't mean it takes less fuel to turn a higher RPM, it just effects how much more fuel is needed, as it always takes more fuel to turn more RPM, because turning a higher RPM equals more work,
each revolution requires energy to move the pistons and rings up and down, to open the valves against the force of the valve springs, the faster you spin the oil pump the more effort is required, same goes for the water pump, alternator, P/S/ pump, fan, rod and main bearings, front and rear main seals, and every other moving part that makes up an engine,
so you must multiply the amount of fuel needed to turn one revolution by the number of revolutions, the difference in the amount of fuel used to turn one revolution will never offset the amount of fuel needed to turn more revolutions, no mater how much more efficient it is at one RPM vs another RPM

now if you would like to test this, just go out to your car and start the engine, let it warm up if you like, then gently depress the gas pedal and allow the engine RPM to increase, hold it there for a few seconds, now release the gas pedal and watch the corresponding decrease in RPM
the only conclusion that can be derived from this is
more fuel = more RPM
less fuel = less RPM
so therefore it must be true that the opposite is also true
more RPM = more fuel used
less RPM = less fuel used
and that is why increasing the gear ratio in the rear axle will always be accompanied by a corresponding increase in fuel consumption at any given speed, or lower MPG