That??s a lot of plant for a little light. 400w is only really good at 16? above the canopy. At best and that means even 3x3 is pushing the area for proper light coverage. The hood you use will determine your light coverage area. Just light one up in an open dark space. Raise it to different heights and measure the light pattern on the floor. That is how you measure the light pattern of the hood. Build your grow area around that information and you will have better light coverage.

For example:
A 400-watt MH from 0? to 12? is about the same luminance say 55000
Same light at 24? the luminance is now about 30000

Still good but the edges of the light pattern have degraded. At 24? and the floor pattern will show you the light is now only good for about 30? square inches of quality light.

Now

Same light at 36? above the canopy and the luminance is now about 1200. See the big loss in just 12 inches more?

Fan leafs block most of the light so nothing below sees enough of the light of day to do any good.

About 16? is average if your plants get too tall just bend them over (if you bend them over the buds get more light and grow bigger). You could crop them to keep them short and bushy you crop between the 4th & 5th node early in the vegetation state for best results.