Michael Muskett was kind enough to respond to my query about drone tuning in a private email, and he has agreed to let me quote his reponse below in this Forum:
"... it is normal on drone instruments to tune the drone (if only one) to the tonic, or keynote (C in the case of C major/minor). The 2nd drone is normally the dominant (5th note: g in key of C). This interval is a perfect 5th, and after the 8ve (ratio 1:2) is the simplest interval, having a ratio of 3:4. It is this tuning of the drones which people find so satisfying and they must be perfectly tuned to have full effect (the drones, not the people!).
Music consists of constantly changing degrees of consonance and dissonance between melody and harmony and between the complex harmonics produced by each string. Certain intervals are sweet e.g. 8ve, 3rd, 5th, 6th. Others are harsh: 2nd, 7th. Therefore, you may add a maj/min 3rd drone to the 8ves & 5ths, as is done on some musettes, but this must only sound when musically suitable. It adds warmth.
It seems perverse to have drones tuned to 2nds unless you particularly want a special effect. If you wish to experiment with different tonalities I suggest you try different modes, as given on page 82 of the Method. And don’t forget the minor keys, of which there are two types. The key in which you play must be in accordance with the drones. i.e. you should not play in A minor when the drones are c & g.
Music is a language, a language that expresses all human emotions with their contradictions and complexities. There are many forms, of which the simplest is folk music, and if you want to play with understanding you will have to learn the basics. This is readily accessible nowadays for all is available on the internet. But it is a great study and at the end of a lifetime you will not know half of it"!