[Harp-L] Strange discovery (diminished chords)

[Jonathan Hill <jonathan.f.hill@xxxxxxxxx>]

I just noticed that draw holes on a regularly tuned diatonic are
exactly the same for 3 thru 6 and 7 thru 10. And there's a nice
diminished chord on 3 thru 5 and 7 thru 9. I don't know why I've never
noticed this before, but its there. So based on this symmetry how do
some of you develop melodic ideas by taking advantage of this setup?
Beyond that, lets say that you're playing non-blues changes (or even
exotic blues changes), how can I use this setup to easily determine
what harp to play and/or what position I should use? I'm gradually
learning to read the guitar chords as they're being played, but its a
struggle. Man do I love being a harp player, though. :-)