Thanks guys. I think the answer to my question is really - there is none. There are guidelines to get you close. I've been reading more of Bryan's triangulation method and the physics make a ton of sense to me. In that case, the location of CG is really a result and not a setting. In other words, you end up with a CG location that works with you and your plane.

I had started with something like Goldsmith's trim process, or one of the similar IMAC trim charts. They start with a CG test, but there is no quantitative answer to where it should be. There are guidelines that get you close.

I think most of us know that changing your CG impacts everything else. So it makes sense that you can't really pick a CG location and stay with it, as you have to balance how the plane flies in all attitudes.

My question then is really where the 25% MAC comes from, but that is another topic! And one I'm sure I can answer with a little research