I agree with you Pleiades, and the header length is the most critical part, as can diameter, however from speaking with the fabricator who created my system, he was explaining that whilst on multi cylinder bikes the end can length is more sound based, the length does have a more pronounced affect with singles, hence why the XTX ones as standard are so long.

Interesting about the metal mule one, I assume they since revised their design?

Mine was based on equal measurments to the standards, and this did result in interesting routing, however I hadn't considered the point you made about the port to outlet length. On my system they are quite different in shape, I guess that will be resposible for the loss

Thanks for sharing the information.