top [countable] the highest part or point of something
at the top of something She was standing at the top of the stairs.
The title is right at the top of the page.
at the top Write your name at the top.
to the top He filled my glass to the top.
to the top of something We climbed to the very top of the hill.
on the top Snow was falling on the mountain tops.
on the top of something He was completely bald on the top of his head.
I was out of breath when I reached the top.
(British English) the top of the milk (= the cream that rises to the top of a bottle of milk)
The wind was blowing in the tops of the trees.
on top of something/somebody: on, over or covering something/somebody
Books were piled on top of one another.
There was a vase on top of the bookcase.
Many people were crushed when the building collapsed on top of them.
According to my research, "on top of something" is simply on something.
So, if you are lying face-up, the book is on your face or "on top of your face"
But, "on the top of something" means "on the highest point of something".
So, if you are lying face-up, then the highest point of your face is the tip of your nose, therefore the book is "on the top of your face" means the book is on the tip of your nose. Maybe, you're an acrobat who has that kind of skills.
This is what I am guessing. I might be wrong.
What are the differences between "the book is on top of his face" and "the book is on the top of his face"?