That's a good general guideline to take your perspective from when looking to place them. Doubling and abundant bowl of fruit on the table (or people in a restaurant),is different than how the balance of a room changes when doubling let's say, a fire place.
Remember Marie talking about incorporating mirrors to help move the Qi down a hallway, or how it can have a non-helpful result if placed facing a bed or inside the front door as people walk in?
Much Love, Shawn