There are no specific physical distance (or proximity) requirements. As a general rule, you should aim to fill out as much of the frame as possible.  

 

If you are recording from a larger distance, we recommend, that the actor takes up no less than 35% of the height of the frame.

 

The greater the distance from the actor (ie the smaller the actor is in the frame), the more you should insist on good visibility, lighting and contrast.