A note about the the head and head position. A sphere has a lousy coefficient of drag - approximately .5. Over the years, to improve the Cd of the human head (and protect it), time trial helmet design became very elongated and large. However, a larger helmet with a better shape may lower Cd but increase the frontal area and total drag force and is heavy, hot and not great at different wind angles.
So new helmets are smaller and offer good protection and better performance at different head positions and wind yaw angles.
Head position...I have attended several aero seminars and done a lot of aero testing. Head position is critical to riding fast. Any setup that causes the head to pop up into the wind is bad. So at a training session, we practice turtling the head by lowering it out of the wind and making adjustments to the setup that facilitates turtling the head.
Even with the most expensive fancy, very tight fitting helmet, popping ones head up into the wind is the kiss of death.