Measuring the tiller, or a tiller measurement from the string to the fades top and bottom can be plus or minus an 1/8" without a noticeable difference if the limbs are balanced out correctly and bending the same....
Balancing out the limbs is what "Tillering" really is. its seldom adjusted with glass limbs and is typically done with tapers and wedges in the lay up. But it can be fine tuned. its a different procedure with glass and carbon backed bows than self bows fine tuning the balance. ones that are out of balance produce a buzz, and have more noticable hand shock.
You have the right idea ptberger....