Probably need to be 3b more from BB. I am guilty of this as well as it is just so easy to call from the BB cuz you close the action. You are going to have range and nut disadvantage on alot of boards from the BB.
vBU and CO probably need to be bluff raising a lot more on certain board textures, especially vs BU. So many guys out there will be opening 40-50% range and just cbetting at will on the flop on certain textures. You already hit on it as well, you may not be defending enough on flop and turn and be fit or folding to much, so need to understand that your range in general is weaker and you need to call down a bit lighter sometimes, although it is 4nl, so not sure how much these guys are barrel bluffing. Anyway, there are certain board textures that you, as the BB, should be XR upwards of 20% and that is against a competent opponent who is betting and defending balanced ranges on a solver. If you arent doing this then you are just allowing the IP player to play perfectly. He can cebt a ton and doesn't have to worry about getting raised and he knows if you do raise you are on a nstrong hand or strong draw and if he has a weaker hand he can just fold.
JJ4r board is always one that I think illustrates this kind of well. It is a fairly static and dry board. So here is what a solver would cbet:
It is ~66% cbet frequency. Bets about 80-85% of its Jx, opting to check back some of the weaker ones for balance. Uses some of the OPs as slowplays, but then opts to cbet pretty much anything with any backdoor equity or overcards to the 4 at some frequency.
So here is the defense that solver comes up with vs this strategy:
Solver raises ~23% on this board from the BB. A ton of stuff really. Not saying you should play solver style at 4nl, but just to illustrate what a good strategy is against a competent opponent would look like
So if you have guys in a spot like this that would cbet 80%. You can just bluff raise a lot. There isn't much they can do. They cbet K7o here and you bluff raise. They are just gonna fold. You might get played back at some versus the crazies, but it works pretty good, I have experimented with it some.