EDIT: I realize now you suggested moving the button sideways, not upwards. Yes, there seems a few millimeters to gain from that. It's so small surgery it's certainly worth trying, thanks!
Thanks a lot for the input.
I was thinking about moving the buttoning point as well.
The first option would be to have the current buttonhole reweaved and a new one made higher up - the suit came with a large swatch of the fabric it's made of, so there is plenty to reweave with.
The second would to have a second buttonhole added higher up, turning it into a 2-button suit. I rather like this option, as it shortens then rather extreme V-zone down a little.
Problem is lapel is cut to roll all the way down to the low button, so adding a 2nd buttonhole higher up would create a slight DB-esque overlap.
I'll see what my tailor suggests.