I've never seen or done any method other than trail and error on this. And it sounds like you have a good start on both the trials and the errors. grin.

Seriously, you can't see your own back, you so can't see how to adjust this very well. And I also worry a little bit that you may be trying to fine tune something that may not need it. Try hiking a few miles with the pack the way it is, then see if it needs fixing.

I once suggested a simply adjustment for my wife's pack, because it looked crooked to me. It took us about three hours and five miles to get it back to where she was comfortable!