Yes ^ that is quite similar to my setup axcept I have the cage sitting very slightly over to the right side as well, in order to clear the handlebar.

I also use a homemade setup with tool clips (broomstick clips?) to mount a bottle cage on the seatpost. I first had it on the front but my legs would lightly brush against it so I started using it on the back of the seatpost. That works OK but needs careful concentration to put the bottle back after a swig especially in pace lines. In the Alpine Classic I even mounted 2 bottles side by side like that.