Rd - turn the barrel behind the rear leg is a good thought - here is a visual - sorry about the dropped frame in this clip but you should get the gist of it....and watch the "curve" of her back being produced by the action of the rear leg and pull back.
RayR....nice gif! A perfect example of a hitter using her front side. The front side action does not act like this if it is simply being guided by the top hand. The front side is working....and working hard in conjunction with the back arm supplying a hammer through the ball. However I think the pull back of the upper body is due to the forward movement of the hips. The upper body reacts to the forward movement of the hips in order to stay balanced and not fall forward.