I'm no hatter but I would say there would have to be a formula in place because on someone with a smaller head the offset would be greater giving the turn a more pronounced look. On a larger head the turn would be less. Either way, larger or smaller the look would be off.
I have been reading how some people like the turn and some do not and I know it has to do partly with preference. However, wiithout a formula in place the look would be off if the hatter was not with you to eyeball it. This may be the reason that some people dont care for the turn on themselves although they like the look on Ford.
Whether using fractions or percentages, a formula is the only way to guarantee the degree of turn for each individual. I know there are other factors, like the shape of someone's head and so on. Now, please forgive me, if this was already covered and I have not read it as yet. This particular look seems to have so many complexions and if there is some formula in place that would help to nail the look for everyone.
![TOH :TOH:](./images/smilies/Indy-Hat-Tip.gif)