a CB is not always a bluff. Say for instance you are dealt AKs and raise preflop. Then you miss the flop entirely. It is a CB and not a value bet because you missed your hand completely and there is a good chance you are now a dog, however, AK could very well be best hand right now so in this case your CB could be considered somewhat of a probe bet moreso than a bluff bet. I wouldnt consider this part of any "quota" or "ratio", as the CB should be a normal part of your arsenal (and depends solely on how many hands you are involved in preflop anyway). I'm not saying you should CB every flop, but post flop bluffing and bluffing with 92o preflop are totally different animals, as are blind steals.

I think if you try to define this as a ratio, you are asking for trouble in trying to improve your game. Bluffing is strongly read dependent. So every situation, hand, table is different.