Strictly speaking, and to re-iterate the comments above. FR is mainly a nut peddling exercise, trying to hit monster hands on the flop when given the odds
to do so. So at FR you will see plenty of reg nits who just sit there and wait, wait and wait for the nuts.
6max is a more looser and aggressive, generally speaking. The key here, is not to play as nitty, but become a more refined player in post flop pots. You have to float villains more, value bet thinly, and go to river a helluva lot lighter that you would be expected to than at FR.