He did as children do, (the greatest imaginers of all time,) in their games when they use a stick for a horse, or organize an entire cavalry regiment out of paper, or, with one extra fold can successfully transform a horseman into a horse. This trend to arouse the imagination of the observer plays a great part in the theatre of today. This is a necessary transition from the material to the spiritual in the theatre of the futur (Vasily Kandinsky).
Jean Cousin, "L'art de dessiner," circa 1768
Head to belly button proportion is for drawing children, why do you find this odd?
In fact most pictures want something, life-size baby drawings are cheaper because of the cost of the drawing paper. Kids who were all too often overlooked and unseen.
What did you enjoy doing at age 4?
It takes a very long time to become young.
Pablo Picasso
As a rule-of-thumb, a good way to deal with human proportions is to ignore the rules.
Jean Cousin, Author of seventeenth century drawing tutorial