The 2" or so of tank depth below the top feed pickup tube also serves as a water trap so condensation doesn't get into the fuel system. It's also a good place for sediment to collect rather than ending up in carburetor jets, fuel pump check valves, etc. In the winter when condensation might become an issue, adding a pint bottle of 91% rubbing alcohol to the tank about once a month is a lot cheaper than a can of Dri-Gas, and just as effective in keeping the condensation to a minimum.
Jerry
