[tucsonjwt]

I heard an interview with a Ford engineer on NPR a couple months ago who said that drivers have an expectation of "fullness" on the gauge when the tank is filled up, and an inclination to run the vehicle to the limit on empty. This is apparently a kind of "getting your money's worth" from a tank of gas mentality.
So Ford, and all other vehicle manufacturers, purposely design the fuel gauges/sending units to overestimate the fuel level when the tank is filled up ("I got my money's worth") and underestimate the fuel level when the tank is near empty ("I better get some gas soon before I run out"). Human psychology in automotive design.