On most of my bows, I have a 1/8" tiller to 1/8" plus a little. When I tiller my own, I can sand on it until the bow shoots parallel shafts with a 1/8" nocking point above level. The correlation is not set in stone, I have seen bows that were happier, for me, with the nocking point higher and still have the 1/8" tiller. Sometimes guys will get changes in the porpoise by messing with the brace heights, but in those cases there may be more things going on than just nocking point height. Sometimes it is possible to use a lower nocking point by adjusting the arrow's feather angle to the bow, as in shoot cock feather in or rotate the nock. The correct brace will always be the correct brace and the correct nocking point is always the correct nocking point, until someone has you try a tapered carbon shaft, then it needs to go up to split the difference. For me it is always easier to establish a nocking point by only adjusting the bottom nocking point, I may add a top one later.