Okay, so I did another roundtrip running the 2013 LR4 to nearly empty.
It was mostly highway traffic, averaging 70+ mph.
This is what I got:
342.9 miles total on my Trip A - I ran for 35 miles with the computer reading "0 miles to empty". The computer also indicated 17.4 AVG miles per gallon.
I filled up the tank, adding 21.296 miles. If I do the math, 342.9 miles / 21.296 gallons, I get about 16 mpg.
--So at 16 mpg X 23 gallon tank - I estimate the total miles could be around 368. So I could have gotten around 20+ more miles.
Here's a quick chart I may use to estimate distance left , even when "0 miles to empty" is indicated:
If AVG MPG is 13, then 23 gallon tank X 13mpg = around 299 miles
AVG MPG 14, then 23 X 14 = 322 miles
AVG MPG 15, then 23 X 15 = 345 miles
AVG MPG 16, then 23 X 16 = 368 miles
AVG MPG 17, then 23 X 17 = 391 miles
These are most like the very "best" case. Things such as climate, road conditions, traffic-stop/go, wind, tides; will all have an affect on actual milage attained.
Take this with caution, as the manual indicates that running out of gas is not good for your engine, so heed the advice of your LR4 computer.