The reason I have plumbed it this way is to ensure the tank doesn't pressurise by allowing all of the excess fuel to return to the main tank correctly since the swirl pot is above the main tank, in fact all of the pipes should be at tangent to the main swirl pot tank, this would help reduce airated fuel by the incoming fuel "swirling" around the top of the tank and then the "neat" fuel filling the swirl pot up to the over flow, this results in an unpressurised reserve of fuel to supply the main fuel pump. Some bag tanks have an internal swirl pot with upto 8 small lift pumps feeding the swirl pot, the over flow being a slot in the top of swirl pot which also contains the main pump and filter. This desigin is used by all top touring car, tin top, single seater race teams, a proven system, Fit and forget.....