Substituting for SET variables

This is really elementary, but it's been a long time(*) since I've had to deal with it:

I set a local variable:
set NRoot=N:\LocalFBu\CRoot\

Which I want to use in something like
set QQSV=cd "%NRoot%%@instr[2,,%@full[.]]" ^ copy /u /p . %NRoot% %&

Much to my surprise, apparently %NRoot% isn't evaluated between back-quotes.
But without the back-quotes, of course, it sets QQSV to the first part and then starts executing the copy command.

How?

Thanks,
BG

(*) I'm still using version...

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