"the instrument is more properly called an octave mandolin"

Well no, not really. Like the modern cittern ('invented' by Stephan Sobell), what Steve plays is a hybrid sort of instrument, based on an instrument that Paul Downse..."discovered in a Brighton antique shop...that became the template for the ones I play and that David Oddy continues to build." (Steve Knightley Songbook.)The tuning is immaterial - I tuined my first cittern in the same way, with the fifth tuned to D (I now use GCGDG) - the form of the instrument is very diffecent to an octave mandolin/mandol aor ahjtever youi care to call it. A rose by any other name......