I'm inclined to urge caution about "running on the fumes".
In addition to the obvious inconvenience of running out of gas in an inconvenient location, there is, in at least some cars and possibly the Insight, a stress condition that occurs when the fuel pump is not imersed in the fuel. The resulting overheating condition can shorten the life of the fuel pump.
I'm very familiar with the marathon event (referenced in this thread by Louis ("SNO779") and other record setting initiatives that intentionally "run dry" as a part of the metrics.
However, all of my data would indicate that the Insight's fuel consumption indicator is quite accurate if the tires are inflated to <46psi. So, what's the motivation for obsessing about miles per tank? You could carry a gas container and perhaps go over 1,500 miles without stopping if that were the goal.
In a twist of irony, I learned an expensive lesson about running with low fuel levels in the tank. I typically drive < 1,000 miles / year in my minivan (which gets 33+ mpg with some moderate hypermiling) and consequently, I don't get to the low price gas station very often. I can't remember ever filling the tank completely. As a consequence, the fuel pump was probably running hot much of the time, and on the way to an alternative tranportation event where I was planning to show my favorite vehicle, the electric assist recumbent bicycle (a very tight squeeze when packed in the Insight) the fuel pump died on a high traffic 8 lane highway. Despite all of the stress involved, I made it to the event on the bike, and also home, thanks to a lift part way from a friend with his Prius. However, there was a > $700 bill for the towing and fuel pump replacement.
Now, with my favorite vehicle (the bike) as the primary mode of transportation (when it doesn't rain or snow), I don't pay as much attention to how many miles the Insight gets on a single tank. I visit the gas station less than once per month. It's interesting and somewhat entertaining, however, to pull up next to the pickups and SUV's (no doubt paying well over $50 for a fill these days) while adding only a few gallons to the Insight under their owners' watchful eyes.