Here's Your Suggested Homework Assignment:
Ear does real work in explaining the Head's Three-Dimensional Position.
As you sketch out several head construction in various positions, notice how a well-placed Ear does a tremendous amount to position the Head.
Take special note of how close the Ear gets the Front of the Face as the Head turns towards a Back View and how close it gets the Back of Head when viewing a 3/4 Front View.
Have fun, my friend!