I believe that the hounds are higher on the SX mast. When I was researching putting the spin on my 18, I found that the comptip part numbers were the same between the 18 and SX, and that the part numbers for the standing rigging were different. From that I deduced that the ~1.5 foot difference was in the metal part of the mast, and that the hounds were at the top of the metal in a similar fashion to the regular 18 but 1.5 feet higher.