I’ve decided to experiment some playing celtic rhythmic backup in (gasp!) standard tuning. I was recently able to spend some time with my friend Aaron O’Rourke and was really impressed with the way he played backup. I think standard tuning offers some really interesting voicings, though the chords are perhaps less powerful than Drop D or DADGAD. In the latter tunings you have a lot of intervals consisting of octaves and fifths, which to my ear gives a bigger sound.
In addition to the obvious first position chords here are a few voicings that Aaron showed me. He uses the up the neck inversions really well, creating cool bass runs and chordal movements that echo the melody.
Hopefully in the future I can post an example with some standard tuning backup.