Well one song that has seemed obscure to me as to "home" note is "Famous Flower of Serving Men". I play it a lot - working round a mock DADGAD done with a shubb C7 capo at the 4th fret and another capo at the 2nd - holding the undetermined one finger D (so it's really F# as it's five frets up) chord. Now the chord of F#minor can be droned away at for pretty much the entire song, but if you think about it the note on the second string is a B, and a fiddle player I used to know was convinced that it was Phrygian B. I just call it F sharp-ish.