Right, it's almost impossible to keep the chest tilted to the sky and make contact with the ball (the ball has to be 3 feet behind the head for that to occur and does not make sense).I get it different:
- You ensure upward alignment in prep by tilting torso back and pushing hips forward;
- You rotate your torso (powered by leg drive) about the tilted axis, keeping alignment to (i.e. towards) contact (i.e. the ball).
By contact chest has already rotated and is now more facing somewhere front/to the side, depending on the serve type:
From what I interpreted from serve doc is that the tilting can occur anytime, but in my mind just before initiating the contact (from the drop position) is the last opportunity.