Start at 7". Shoot the bow and listen to see if it is loud. If it is, increase the BH by twisting the string a couple of twists to shorten the string. Keep increasing the BH a couple of twists at a time until you reach the point where the bow is the quietest and go past it just a bit. Then go back to the BH where your bow is the quietest and that should be the BH you should use. When I don't know what the recommended BH is for a bow, as recommended by the bowyer, that is the procedure I use to establish the BH I'll use for a given bow.
Bill