My big bad truck has its soft side. It politely counts down the miles left in my tank. But, when it hits zero, I still have a bunch of miles left. On average, I can go 50 miles after the countdown ends, with the most being 55 miles.
my experience (not a Lariat, so no trip computer) is that when Ford lights come on, there is usually three gallons left in the line. As a result, I don't trust there to be more than 50 miles or so worth of fuel once the light comes on.