For moving the controller, Jason is correct.
For pointing at the screen, Null is correct.
Unless, of course, the receiver is inside the controller... which would mean distance from the screen is not a factor for movement.
Also, if the controller's projection cannot exceede a certain angle (for example, if the receiver could not read a controller pointing at 45 degrees), it would be easier from a distance, as a smaller angle moves a greater distance.
I think the further you can get from the TV without making it too difficult to control, the better. And, this probably depends on the TV's size. Think of it like turning up the sensitivity on a first person shooter (i.e. Halo). The more sensitive, the easier it is to move. However, if you set the sensitivity higher than you're capable of handling, you'll find your screen flailing around making it
difficult to control.