[snowrx]

If you run past the estimated range, the display will flash a "Refuel" message and stop showing range. I went 2-4 slow miles past "Refuel" and ended up putting in 12.04 gallons. Another fillup with 6 miles of range showing took 11.5 gallons.
I would not look at these as hard numbers, because the ECU is probably estimating range based on driving up to that point in time, so if it's uphill all the way to the gas station, your range may be less than indicated.

One early delivery car ran out of gas, which resulted in a bunch of codes thrown and a trip to the dealer, so I would not push the tiny tank to hard.

 

[snowrx]

In my area gas stations can be 20-30 miles apart, so being able to judge the gas remaining is a peace of mind thing. Like, do I need to turn around, or do I sweat all the way to town hoping I'll make it. The GRC gauge/estimation seems to be accurate enough to work around the tiny tank.