Ahh, I got it. So, in soil, since the roots will grow down, that is why you need it to be deeper rather than wider. However, in hydro, since there is no soil, the roots can grow any which way they want while suspend in the water, so as long as the competition isn't too heavy for the nutes, and there is enough oxygen for the given volume of water, it doesn't really matter. This has to be how they are putting plants in containers that are only 6" or so deep in hydro grows. Is this correct?

thanks!