Wow, interesting question. If you're connecting it to a B&O video system, it seems that you'd want the eye to be as close to the screen as possible, since it is acting as the ambient light detector. Plus, it seems intuitive to point the remote control at the screen when you want to change channels, so the eye nearby the screen makes sense.
If the eye is running a link room, you'd want it to be in a convenient place and height in your room where it's easy to operate manually.
Maybe about the height of your light switches.