According to this link, a G-mixolydian melody "sounds good" (i.e. there are no jarring dissonances) when played over a Gsus4 chord, and a D-dorian melody sounds good when played over a Dm7 chord. M.Ted mentioned some other "sound-good" relationships of this kind. I though he was off topic, but maybe he was right on. Is it relationships of this kind, besides the obvious ones (X-mixolydian over Xsus4, X-dorian over Xm7) just mentioned, that Peter T. is trying to work out ?

T.