that way seems kind of inefficient cause you won't have a lot of room for other equipment. it's really not that big of a deal to have the lights overshadowing eachother; with 4 plants per light you be getting plenty of canopy coverage and footcandles per square foot. just rotate your plants every couple days.
think about it this way. 6000w has a footprint of 10'x15'. there's now way you will be able to comfortably fit that footprint in a 16'x12'9" room and still have space for other equipment and to move around. especially if the door opens into the room.