Flop situation

Here is a situation that comes up often for me when playing Hold'em, and I want to address it correctly.


The situation is this: (to simplify, let's assume that the SB folds, and his bet is taken as the rake)


1) Regardless of whether or not I have a quality hand in EP or am in a steal position, I raise and wind up isolating the BB.


2) The flop does not help me and the BB checks.


3) Given that there are 4 small bets in the pot, when evaluating whether or not to bet, should I be thinking:


A) I am getting 4-1 on my bet, so if he folds 20% of the time, a bet is surely profitable.


B) He is getting 5-1 on his call, so if he folds 16.7 % of the time, a bet is profitable.


Which is the correct way to evaluate the situation when I am betting as a bluff or near bluff? A or B?

If you lost every time that he called you, then a bet is profitable if he folds more than 20% of the time.


0.8*(-1) + 0.2*(4) = 0.