When I got my 400W metal halide, I set it up in a corner of the room that still houses my clone and veg plants. The light was so strong and I only had about 4 or 5 plants under it, I didn’t think I’d need to worry about how much light they got. I built what is now my veg chamber from 2x2s and plywood. I painted the walls and floor white (as I did in my new flower room). I wasn’t disappointed how they grew in the corner, because it was only temporary. I was disappointed in my yields in both rooms. I had gotten bigger buds in my 2x3’ closet. I had covered the entire closet except the floor in Mylar and had gotten much bigger buds out of it.
I bought 100’ roll of 3’ wide, thick Mylar online. I stapled it into my veg chamber and duct taped it to the walls in my flower room. My yield went up by at least 50% on the next grow. You can’t discount the importance of reflected light.