In 2004 we bought an Armada. Had about a 28g tank. We never had a problem running out of gas. When the fuel light came on there was maybe 2 gallons left, about 30 miles of gas, so you stopped asap. Too many @$!#& were running out of gas in these cars pushing their luck with the gas gauge and filing complaints. So nissan recalls all the armadas and changes the sending unit. Hacks up the carpet in the process. Imagine how much this cost Nissan.
So now my wife runs out of gas 3 times after this recall after getting used to having 5 gallons remaining after the light came on. Anyway...
The manufacturers cannot win, if they make gauge precise, people run out out of gas and/or complain. If they add safety margin, people run out of gas and/or complain.
So if nissan recall happened with 28gallon tanks at ~15mpg it would probably happen with 17.9 gallon tanks at ~20mpg. That's why you have ~3.5 gallons remaining when fuel range displays 0 miles. Manufacturers point of view is that is better to havecomplaints about having extra gas than not having any gas from side of the road in sub zero temps. Designers also have to take into account hilly areas.