Jim and others were quite correct that adding oil does nothing as far as changing nitro (or methanol) percentages because you tune the needle to get the correct flow of methanol/nitro into the engine.This is all the engine wants to know about. A simple example is a fuel with just methanol and oil. No matter how much oil you add the engine is always tuned to accept a certain flow of the methanol through it. The engine always runs on 100% methanol and the oil just gets carried in with it. Now mix a blend of 50/50 methanol/nitro with no oil. This is the fuel for the engine although it wouldn't run for long . now add any amount of oil and the fuel part of that blend will still be the same 50/50 mix of methanol/nitro. You just have to open the needle more to allow for all that oil.

The last part of that fuels link is incorrect when it comes to calculating percentages by adding oil because it's treating the entire fuel blend as one thing, the way it's normally done. What's generally not recognised is that a fuel blend is just that, a blend of oil and fuel.