Having heavy floats, we had a pair from a customer 912 weighing 12grams just last week, would exacerbate carburetor problems in hot weather.
One reason not to point the inlet and outlet down on the mechanical fuel pump is it would make it more difficult and maybe impossible to get rid of vapour, vapour likes to stay at high points in a system.
Placing the electric boost pump in a cool location close to the tank would be ideal, not in the engine bay for heat soak reasons.