Lifehacker has published an interesting article on the position a wi-fi, especially those at home or in the office. Best quote of the article below.
"but the gist is that when you pick a spot for your Wi-Fi router, the signal bounces around the rooms of your home. Eventually, though, it will settle in a calm, repeating pattern. Much like the surface of a still lake."
They also found this app that helps visualize this as seen below.