MV-- yes you are partly right-- the degree of recirculation depands apon the model of 737. Passengers do notice the smell of cigarette smoke sometimes leaving the cabin cew with some difficult lies to tell!
My elation at the recent move by FR management over the smoking issue was short lived! My FOs tell me the bulk of smoking Captains have completely ignored the recent instruction (FCI). Maybe the next move will have to be sponsored addiction therapy by the company! Only yesterday I flew a 737 with an overflowing ashtray on the left side!