Thank you both, that is very helpful and useful to hear; at least it is a known thing then, I wasn't sure if it was simply just my ineptitude.
On the strength of this I did some more forum searching and found passing references to using a dummy x-server - that was on headless setups, which isn't quite the situation here, but may be some kind of answer possibly, if one knew how to sort it all out.
Yes, realVNC is rather good, but I think there were some issues with even the free version needing to access their licence servers which (on my setup) it can't necessarily do. But having done some more tests, forwarding by x11vnc, x2go's screen-sharing extension, and TigerVNC's scraping server all seem to share the existing/real screen so I'll probably go with one of those for now, whenever I want to use MC. If I decide to move to a headless machine or begin to use MC as the main software, I'll try to reconfigure things more optimally then.
Thank you again for the help, I don't entirely understand the details but do feel less vague about things now.
Cheers,
Kev