If you can mix out the coupling with the radio, and the model flies clean at all airspeeds with the mixes, personally, I'd leave it at that. In many cases, the mixes change a bit with different air speeds and this is where modifying the air frame comes into play. You're going to need to get the mixes close and compare the behavior at different flight speeds. Then, decide if the difference, if any, warrants cutting into the air frame.

John