Currents bar is on deck 13, in the middle of the ship, outside, just forward and above the adult pool, above deck 12 elevator lobby. The smoking section is port of said bar on 13. To avoid any smoke wafting down/over to a deck 12 veranda, I would book one as forward as possible. The only caveat is the more forward you are the more motion you feel. And yes, I felt a difference from one end of hall on 12 to the other.
Deck 12 port cabins start at/above smoking section so midship is n/a, can only go forward.
HTH