Hypersmurf
Moderatarrrrh...
If you want more realism, you'd let creatures see beyond 20 feet, but not far; you'd also have to severely restrict vison within the 20 foot radius, though.
Once you hit 1/2 concealment, you have to be within 5' of something to see it at all (Obscuring Mist spell).
I think your table there might be a little too severe... the guy with the torch wouldn't even be able to see something fifteen feet away from him without low-light vision...
-Hyp.