I too transitioned into aquaponics from hydroponics, and as such I sorta kept some of the same depths that worked for me in hydro. Currently I'm running continuous flow at a depth of 4" below the gravel, sorta DWC with rocks no siphon, but I do draw the water off the bottom.

Although I do raise the water level to 1" below surface while direct sowing seeds, and then lower it a few days after germination. Bit unorthodox but it's working rather well for me.