This is a simple question that really gets into the way our engines work. First thing is that the fuel (the methanol part) ignites because of a chemical reaction between the methanol and the platinum that's used in the plug coil. This is actually a catalytic reaction which just means that the platinum doesn't get used up in the reaction but stays as it is, in the coil. What the reaction does though is to put heat from the reaction back into the coil to keep it hot.

But two things are needed before this reaction can take place. First thing is the coil has to be hot enough which is why a battery is needed at first. The second thing is there has to be enough pressure of the air/fuel against the coil. This pressure packs more molecules of the mix against the platinum and this comes from the compression ratio of the engine. These two things, heat and pressure, combine to start the reaction. With more heat you need less pressure and with more pressure you need less heat. By combining these two variables you can set the point at which the mixture ignites, in other words it sets the ignition point.

Raising compression with the same heat range plug advances the ignition point but the ignition timing can be retarded back to where it was before by using a cooler plug. If compression is a bit low for the fuel being used then the timing can be advanced by using a hotter plug. This can only be done by trial and error but with an engine driving a constant load (on a dyno or driving a prop) then basically it's the plug that gives the highest revs because the closer you are to the perfect ignition timing the more power it'll give.

Just a minor point but we don't really have pre-ignition because (hopefully ) there aren't any glowing hot spots other than the plug. We can get detonation though if the ignition timing is too far advanced by using a combination of too much nitro, too much compression and too hot a plug.