DWC water level for seedlings and throughout growth

i can't see where the bottom of the netcup is in your pictures, however in my DWC setup, i keep the water at a point where they just do not touch the netcups (barely).. the airstone will create the bubbles that splash some water to the bottom of the netcup to ensure that the rockwool gets wetted, so the root will not dry out, but aren't overly wet (i.e by touching the water).. that's how i keep it from seed to finish (obviously after a short while the roots will dangle into the water, and will then start using up nutrient solution, but when i refill the reservoir, the maximum is just below the netcup)