It depends on how hard i ride. I tend to ride in low gears at high rpms, and accelerate hard and fast. This takes my gas mileage down substantially. Its a sacrifice I'm willing to make. If i wanted to get 200 miles out of a tank I would ride easy all the time.
It really depends on weather and road conditions as well as my mood - as far as how hard i ride - which really determines how far my tank gets me.
Usually around 130 - 140 miles per tank. I've gotten up to 180 miles though before reserves comes.
And yes i notice my fuel gauge varies. If i'm parked on a hill, my sensor reads less or more than I actually have in my tank. And when not moving, my gauge reads less than when I'm at 6,000 rpms. Therefore the reserve starts flashing when I'm stopped, the F-trip starts. I'll start moving and the F-trip stays on, but the reserve stops flashing.
So depending on the angle of the slope your bike is on, and the rpms - your fuel gauge will fluctuate accordingly. That would explain why the reserve stops flashing or your fuel gauge goes up and down.