The 400 should have no problems covering the footprint, especially with flat white walls, you will get a lot of reflection. With my Scrog, I did a stadium-type because I thought the buds on the edges wouldn't get as much light, but it turns out now that the buds on the edges are the biggest! No worries with the footprint, IMO, but if you feel necessary, just throw a couple of those cfls toward the edges.