I think the only thing Marie is insistent upon is to never burn candles in the NorthWest because that is the gateway to heaven.
There was one part of the course where she told about a lady who loved her blue candle and put it in the north because blue represents the water of the north. She was disappointed that she didn't get the results she was looking for, so she asked Marie. Apparently, by burning the blue candle, the flame overpowered the blue in the candle, and cause the candle to represent the fire element, even though it was blue.
I think that if you burn the candles, the fire element will overpower whatever element it is supposed to represent; therefore, I think you should limit them to earth areas (SW, C, NE) because fire produces earth, or the fire area (South).