I have tested both several time, +nn-nn+ does produce more than the opposite. Ask yourself this question, when electrons flow, in which direction do they flow? Positive to negative or negative to positive? That is the answer as to why +nn-nn+ works better. Electrons flow from negative to positive which causes the n plates to take on a negative charge. If you put the Negative plates on the outside, then only one side of the plate is being used where as in the middle both sides are being used as well as the neutral plates. Other than that, the flow of the water is different as well. Thats the best way I can explain it.
2006 Ram, 5.9 cummins HO. 4 cell design, 1.5 LPM@30amp, 24.3 MPG