Sure, you can mess around with compression ratios but for the average modeller this is just another variable they can do without. With something like the Hanno you're getting into a specialised competition area where the skill level is quite high and most of the basics of engines are well understood. The main point with nitro is that the more that's used in a fuel then the less compression it can handle before it detonates. This doesn't actually mean that if an engine's got low compression that it NEEDS high nitro, just that it's capable of handling more without damaging it.

There's really only one way to find out how much nitro any engine can handle and that's by using a good tacho. Start with a low dose and check the peak revs. Then run another tank with a higher % of nitro and check peak revs again (after it's been retuned!). Keep doing this until the revs stop increasing and you've reached the maximum amount of nitro for that engine BUT only with that particular compression, plug and prop. If you change any of these then you have to redo the tests. Unless you're in a competition where you need the absolute maximum power then it's not necessary to do any of this, just use a fuel that contains anything from zero nitro up to whatever the maximum recommended by the manufacturer.