Hi,
Not quite: In reference you can put the any file, such as the original that you have been working on as the Reference, and then put the soft-proofed virtual copy in the Active half. The soft-proofed visual copy is already adjusted for the paper profile so of course it is not a soft-proof of a soft proof.
I am not sure why you would want to compare soft proofs. The only valid comparison is that with a prit. The soft proof simply has to match your original adjusted original image. The soft=proofs for different papers may/will have different adjustments, but they should look like your original image.