Almost invariably travel two up, my wife used to hold the bottle in her hand, but for 200-500 mile days on tour this was not good for her.
The position of the bottle without the tank bag i.e. my side of the bars works great for a quick drink at traffic lights, so in my face is just where I
need it.
The cup holder can hold a thermos flask instead, which is guaranteed to keep hot for 16 hours, in case we want to stop for coffee.