http://www.tap46home.plus.com/mechanics/ This is the best discussion I have found, although he keeps moving his site around. I've used it for many years, and have yet to find exception to his thinking. To be fair, he generally sumarrizes and builds upon work published by Kooi.
The section titled Bow Mechanics - Tiller dicusses what you are asking, but the whole dang site is, I would argue, prerequisite reading for those interest in bowyery and tuning.
The rule of thumb I follow is, farther above dimensional center, more positive tiller. Since three under tends to put the forces closer to center the "even tiller for 3 under" rule most bowyers will quote seems to follow. But it's not just a simple, single element. The tiller shape matters too, and nock point obviously can be used to tune out or in more or less tiller.
After making dozens of bows, I can't honestly say I've found a method or formula, other than trial and error, that works in all cases. But the general rules of thumb do seem to apply.