Lets restate what happened for those who can not (or will not) read.
3 times I drove 20 to 70 miles on flashing fuel warning and bought less than 10 gallons. Gauge is now calibrated and behavior believed to be understood.A few weeks later the light started flashing and ONE MILE later the ICE was dead. The gauge was taking measure of fools who trust it. Yes, the light said the engine might run as long as 70 miles based on past experience, but 1 mile isn't any warning at all. And 1 mile sometimes,
70 miles sometimes, isn't very reliable.I continued my analysis and concluded the gauge falls about 1 to 2 gallons slower than actual (miserly) consumption. Let it sit over night and the gauge catches up. This is normal for ANY CAR, and no other car than the Prius has a bladder gas tank so its not a bladder thing.
The only thing different is that most cars use a thermistor in the gas tank for the low fuel warning light. This thermistor is very accurate, fast, and reliable. Apparently the Prius does not use a thermistor.