This principle emphasizes that there should be no space behind you. It has nothing to do with the wall or window in front of you. Those are just examples I used to explain according to the original post.

If you're concerned about the window's position, ancient Feng Shui advised the window should be located to your side, specifically on the side of the hand you don't use for writing. I think their reasoning was: this way, your head and the hand you use for writing won't cast shadows on the area where you're writing.