I'm still pondering on this, but I reckon I have it cracked.
I was inspired by this
For this fabric
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using the edge along the bottom edge, but I've now realised I don't have enough "edge" for my edge.
So, Plan B - use the edge along where the button flappy bit is on the pic, and along one of the edges of the seam that runs from the neck to the hem. I just need to work out which side of that seam to put it... This means off grain pieces, so I'm inclined to put it on the smaller right hand piece, overlapping the left with the flappy bit. Do you think that will look right? I think it will, as with the diagonal seam it will in effect be hanging down -ish.