Question about gearing and fuel economy

Admittedly, fuel economy isn't my top concern when I'm riding my Ducati Panigale, but I noticed a big difference in how many miles I'd get out of a tank depending on my average RPM. Obviously, driving hard will get you lower gas mileage, but my question is this: If I'm cruising on the highway, engage the clutch and idle the throttle, then I'll slow down at some rate due to wind resistance. If I were to downshift and roll off the throttle so as to perfectly match the deceleration as the scenario above, do I use more or the same amount of fuel? Put another way, If I do 2 trips with the exact same acceleration and velocities except one trip I keep the RPMs low and the other trip I shift later and keep the RPMs higher, what is the difference fuel consumption? Any engine experts that can provide any insights?