If I set my RNC compressor's threshold knob to 0db, and use the
fastest attack, fastest release and highest ratio of 25:1 (in regular
mode), I notice that on my computer's soundcard meter (delta 44 set at
+4dbu input sensitivity) the signal gets limited to approximately
-12db.. This seems to indicate that if I bypass the compressor and set
the preamp gain so that the signal to the point where it just misses
clipping my soundcards input and then insert the compressor, the
compressor will probably have an input signal level which is way
higher than what it considers 0db...

Will this degrade the compressors performance? Should I concentrate on
providing a signal level to the compressor which is close to what the
compressor considers 0db, and then set the compressor's output gain to
a high value like +10 db or whatever gain it is needed for the
soundcard to show a signal level closer to its own 0db mark?

I wonder if the RNC supernice mode is dependant on signal level that
it receives and if the compressor receives a signal much greater than
what the compressor considers 0db the super nice algorithms would
provide unexpected results...