Hurrah! That seems to have sorted it. Thank you.
Some initial kerfuffle after first selecting "Display 2" in that option. "Open in Theater View" was still selected, but "Standard View" had last opened and shut on Display 1. So on exiting Theater View to Standard View, Standard View then hopped to Display 1. Not a problem, of course, but for the fact that Standard View seemed to be so confused by this that it froze. Had to shut everything down via Windows Task Manager. Tried again. Same thing. Standard View still frozen on Display 1. Which left me with no way to move Standard View or indeed adjust any settings since, whenever I got to Standard View it was frozen.
Only option was to disable Display 2, forcing both views onto Display one, select Display 1 in the tree view options, uncheck "open in Theater View". Then enable Display 2 again. Pull Standard view across to Display two. Shut it down then re-open it to make sure it stays on Display two. Then select Display 2 in the tree view options. Then select open in Theater View.
All seems to be working now, but ye Gods it didn't make things easy.
Thanks for you help.
Cheers
Mark