Thank you for the reply, Chris, and yes, that helps a lot!

It's a song I'm writing. It has an echo/overlap for about a measure between the end of the last line and the beginning of the first. Neither chord alone works, nor does any combo nor does any other chord in the key. It seems to want the chords to overlap as well as the melody.

Like a choir singing in the round, but only for a measure, and on different chords.

Put yet another way, when I play my fingers intuitively try to reach for both chords at the same time.