A few ideas for you:

A 400 w light is not enough to cover 4' long with that type of hood.

Second when the roots start to show out the bottom of the net pots they will die and affect the plant's growth. You can use pond liner to cover them from the light.

Third you may want to rotate your plants in place and in their location so they can have a better chance of sharing quality light or the ones on the far end will grow toward the light and block the others.