I'm not sure exactly how yours is set up. If you go to the 'Technical info' section of this site, you will find a picture of a triangle stern travler, and a description of it. Basically this triangle is fixed and the top block is about 22" above the deck. This height is varible as some DS's are set up with the max deck to gooseneck 24". Others are set up as low as 18". ( the factory didn't always make them the same.) so the traveler height will be a little different.. On a calm day, put you main on and with no boom vang pressure, sheet the main in until the main sheet , block and weather traveler deck block form a straight line, and your boom is 10 - 12" below the center line. This will give you a very good starting point for that traveler.
phill