I run mine down to E a lot. I had them both down to E or even a hair lower and was a little worried the other day coming home on the interstate and it still only held 16 in the front and 14.5 in the rear. May be just the way my gauge reads, I don't know. It has been like that as long as I remember

 

This is how i see it, the less fuel in the tank, the more particals floating around, the harder it well filtrate. Ok, the more fuel, the less particals, the easyer to filtrate.. Pretty much what oldbird said.

 

But in my own theory lol

 

Darin, i've run my down past E where you can see black inbetween the needle and the red part of empty. Once I was really pushing my luck to make it to the next exit (my security blacket was empty to) so I ran it until my fuel pressure gauge started jumping around. I hit the switch and was suprised at how fast it leveled out with the fuel from the other tank.