To do DWC proper you need plenty of aeration, not just to introduce O2 to the water supply but because of the agitation on the water surface. This area of agitation, or flying water drops, is like a small aeroponic environment. My 5-gallon DWC setup throws water droplets higher then 12 inches.
The reason you leave a gap below the pots is to take advantage of this aeroponic environment. Healthy roots will become fuzzy in that aero layer, and fuzzy roots soak up nutrients like crazy. Heavy drinking roots will reach down into the res, but the roots in that mini-aeroponic environment can account for a significantly larger root surface area due to microscopic efficiency.
The agitation above the water surface is what sets DWC apart from other hydro methods. It is better to have more air pump power then to use water pumps with feeder tubes.
Soaked stems are also prone to rot.