I've been using Gravity Screen as well, but I find it has some issues and the way it works doesn't seem to be the most efficient.
For instance, when using the phone while lying down, an the found is at a 180d angle facing downwards, the screen goes off immediately. Sometimes when I get a notification (with active display) and I pick up the phone, the screen goes off immediately. And, there's no reading mode like screebl had.
Have you found another app?