Hi again Sandy,
I hope the posts by the others were helpful. Maybe a little confusing.
My suggested method to determine harness line position and rig balance is something I
try to convey to as many sailors as possible.
It makes you a bit more sensitive to when the rig is balanced, and when it's not.
Then you can make little changes, on the water, to improve the balance which makes
everything about your sailing session work better, as you do not have to worry about the rig.
There are other methods, and there are some "imbalanced" methods that the racers use with the really big rigs to make sheeting in easier.
For now, just try to get your lines to where you can sail along fully sheeted in with your rig raked back and down with no hands on the boom.
This makes one less thing to worry about.
The suggestions by the others here probably work for some rigs (their rigs for sure) some of the time, but setting your lines and being able to tell when they aren't quite balanced, works all the time with all rigs.
Hope this helps,