Zones are a concept, not clear defined lines. Rooms are a good point to find zones, but a second level reachable via ladder could be another one in the same room. Hindresses like a moat, a hedge or a fence could be good indicators for another zone. A podium, overturned shelf, a big pile of junk or the room before and after the tavern counter could be new zones within one room.
It all matters, if they forfill cinematic or strategic purposes in the scene. If you build up a fencing duel up the stairs of a tower every few steps could be zone or every storey or the whole stair is one zone. It depends where you wanna end: If you want the fight to swing up and down: many zones - if you want the final confrontation on the roof overviewing Upsala, while the sun bathes the city in blood-red light....: just one or few zones.