My flatting range IP varies depending on position of pfr and player profile. also depends on the aggression of the blinds. If they have a high 3b or squeeze % then it is not so profitable. However if they call often it can be super profitable.
My 3b range is made up of the best hands I am going to play and the best hands I was going to fold, my flatting range therefore includes those in between. How wide this is however, as i said earlier varies by player.
You want to be flatting more often against fish/recreational players (look for players with <100bb stacks, limping pre etc to make general assumptions if no stats) and even more so with fishy players in the blinds.
Sorts of hands I will flat (not always) are:
I will also include some of these into my flatting and open range against regs to balance.