Wasn't able to find any theory behind this concept. My guess is
fuel pressure. Anyway, this concept came from many drivers
commenting about it. 1 actually did a test, which you can try out.
Drive your car normally for half tank, pump and check FC. Then
drive your car for full tank, and check FC. What most people notice
is after half-mark of car, the fuel dropped faster.
Then again, if you are a natural light footer, I guess this might
not work for you. 