i assume the OP was about cash games??
Anyway imo, it depends what your opponents know about your game. If you have been playing small pot poker recently, like checking behind good, but non nut hands in position for pot controll,( like i somtimes do) then your value bets are not going to be called as often because your opponents wont pay you off with a hand that cant beat top top. So i guess your bluffing range needs to be higher on the river for someone to look you up, and give you + EV. Another thing i think, and maybe i am not alone, but it is good to get caught bluffing everynow and then in a session, so you can value town a calling station in another hand later on in the session. I think this is one of the big differences between cash and tourneys. And maybe in cash games you should look for plays that are going to make you more money in long term.