Say we're vs this range on the flop:
Board: 8♠6♣J♣
Equity Win Tie
CO 21.98% 21.67% 0.31% { Kh9h }
BU 78.02% 77.71% 0.31% { JJ-77, AQs-A2s, KTs+, QTs+, J9s+, T8s+, 98s, 87s, 76s, 65s, 54s, AQo-ATo, KQo }
144 hands so far. With how much I bet I need to be successful ~42% of the time.
So with hands of at least BDFD value we get total of 111:
Board: 8♠6♣J♣
Equity Win Tie
CO 21.60% 21.32% 0.28% { Kh9h }
BU 78.40% 78.12% 0.28% { TT, 77, JdJh, JdJs, JhJs, 9d9s, 9d9c, 9s9c, 8d8h, 8d8c, 8h8c, QTs, 54s, AsQs, AcQc, KsQs, KcQc, AdJd, AhJh, AsJs, KdJd, KsJs, QdJd, QhJh, QsJs, AsTs, AcTc, KsTs, KcTc, JdTd, JhTh, JsTs, As9s, Ac9c, Jd9d, Js9s, Td9d, Ts9s, Tc9c, Ad8d, Ah8h, Ac8c, Td8d, Th8h, Tc8c, 9d8d, 9c8c, As7s, Ac7c, 8d7d, 8h7h, 8c7c, Ad6d, Ah6h, As6s, 7d6d, 7h6h, 7s6s, As5s, Ac5c, 6d5d, 6h5h, 6s5s, As4s, Ac4c, As3s, Ac3c, As2s, Ac2c, AdQc, AhQc, AsQc, AcQd, AcQh, AcQs, AdJh, AdJs, AhJd, AhJs, AsJd, AsJh, AcJd, AcJh, AcJs, AdTc, AhTc, AsTc, AcTd, AcTh, AcTs, KdQc, KsQc, KcQd, KcQh, KcQs }
He would probably fold 22% immediately. However he may still fold stuff like As2s or AcQd so we can count on a bit greater FE. I agree that cbet alone on the flop isn't profitable so c\f is the safe line for sure.
However let's consider 2nd barrel. I need ~40% once again. I assume he would continue with draws, TPs, second pockets. If he folds eights we almost have necessary FE. If not, we have about 30% FE as he continues with 76 of 109 hands:
Board: 8♠6♣J♣ 4♠
Equity Win Tie
CO 10.62% 10.62% 0.00% { Kh9h }
BU 89.38% 89.38% 0.00% { TT, JdJh, JdJs, JhJs, 9d9s, 9d9c, 9s9c, 8d8h, 8d8c, 8h8c, AsQs, AcQc, KsQs, KcQc, AdJd, AhJh, AsJs, KdJd, KsJs, QdJd, QhJh, QsJs, AsTs, AcTc, KsTs, KcTc, QsTs, QcTc, JdTd, JhTh, JsTs, As9s, Ac9c, Jd9d, Js9s, Td9d, Ts9s, Tc9c, Ad8d, Ah8h, Ac8c, Td8d, Th8h, Tc8c, 9d8d, 9c8c, As7s, Ac7c, 8d7d, 8h7h, 8c7c, As6s, 7s6s, As5s, Ac5c, 6s5s, Ac4c, 5c4c, As3s, Ac3c, As2s, Ac2c, AdJh, AdJs, AhJd, AhJs, AsJd, AsJh, AcJd, AcJh, AcJs }
If he raises we can safely fold. If he calls we can consider 3rd barrel as he probably has weak range given the board is wet. I agree it's a marginal situation with no immediate profit from 1 or 2 bets but is it a good board to consider all 3 barrels as when opponent is passive he's probably weak and will have hard time to call all 3 barrels. Or would you better choose spots with some additional pot equity like BDFD+OC? I mean does our hand matters that much in such spots when we rely mainly on FE?