Quote:

If the returned fuel returns below fuel level it will have higher back pressure and it will vary with how full the tank is.



do you realize just how insignificant that is?

the static head pressure of water (specific gravity of 1) is .433 PSI per foot or .036 PSI per inch. the specific gravity of gasoline is around .75 so you multiply the above numbers by .75. that gives you .352 PSI per foot or .029 PSI per inch. even if there was a foot of depth in the tank that return line would only see .352 PSI of back pressure