Robin.K - I have the same issue
Try the
Quick Preferences plugin. When I tried using it it didn't work for me in a procedural sense, but that was a long time ago when I was a calibre neophyte - if I were to try it today it could well do what I want.
So my workaround is: I add 'books' to my Media library (where I want 'copy') via an installation of calibre portable. Portable has a separate configuration folder where the Tweak settings etc are held. I only use it when I am adding 'books' to that library.
BR