RCA Shorting Plugs vs Caps non-shorting ?

I have had Cardas RCA Caps on all unused inputs in my preamp for some time. I recently bought an inexpensive bunch of gold-plated Chinese RCA Shorting Plugs on eBay (Cardas has a much more expensive version). The Shorting Plugs had a dramatic impact on dynamics seemingly reducing the noise-floor. (I seem to remember that back in the 60's/70's, shorting plugs often came with the preamps and integrated amps I had then) Are there RCA jack locations that can only be served by Caps vs Plugs? The second Preamp Out and Tape Out would be candidates for Caps vs Plugs, but all other unused jacks should take Plugs. Is that correct guys?