Sorry, I can't remember the thread where I asked about the problem with properties dialogs for Nexus dock items coming up on the "wrong" display...
The answer is to have the main Workshelf config dialog visible, while it's visible, all the dialogs appear in the middle of that dialog position. Move the config dialog, the other dialogs follow like little lost sheeps

Hope this helps someone else (but I think probly not!)

Good! But I've fixed most of the dialog position issues with multi-monitor systems on 8.2 too!