Playing with fuel transfer limitations like no transfer through heat shields, I am testing out using EVA construction to fit the FTX-2 External Fuel Duct to transfer fuel between 2 tanks with a heat shield between them. What I found was, with only 1 ducs fitted, I can not transfer fuel but with 2 ducts, 1 going in the other going out, I can transfer all day long. Is this intended? It makes no sense to me as 1 way is all you need for say, the old aspargus staging.. Anyone have any thoughts?