No joy, I'm afraid.

Sorted that out and any difference is very minimal.

Well - I'll make a metal notched straight edge and check the fretboard.

See if frets are all level Then see if the frets are a little higher on the Low E side.

If that's all as it should be... then as you suggest it's taping at the 12 or 9th fret and lightly go over the 22 to 11 frets.....