what you need to do is be more aggressive. raise all pairs preflop if you are the first to act no matter what position, if raise and you have a small to medium pp calls if you have good odds
. c-bet a lot more then you would at 2nl, i advise in adding "fold to c-bet" on your HUD, also, add "continuation bet" to see how often your opponent c-bets the flop.
the thing is they get tighter at this level but not much better, they will c-bet a lot more however most of the time they won't continue the aggression on the turn if they don't have anything really good like at least tptk type of hand, so you can take it down a lot of the time. also, this so called regulars can be 3bet a lot more often in position, they only continue with their top of the range, AA KK QQ AK and sometimes JJ.
also, i advise on opening 4xBB preflop.