It all sounds very scientific and complex.

In actual use, I don't mess with it. If I'm blowing plugs (too much compression) I run a colder plug, or a smaller prop. I usually always run the same fuel. If I have a prop I really like, and am still blowing plugs, I might put a shim in. Not really rocket science, or something to dwell over. After a while, you'll become accoustomed to what sounds right and works good.