The plant gets like 1% of the oxygen it needs from DO in the water. The rest comes from the hanging roots. You simply can't get enough o2 into the water. There is a DO limit. The vast majority of the root mass is below the water level.
How big are the net pots? I run 10" net pots and I keep my level 2" above the bottom of the net pot. Because of how big these net pots are it's best to keep the water level above the bottom. Smaller net pots are best kept under. My plants drink 2 gallons a day. It drank less when I kept the water level below the net pot. So yeah, if you use large net pots keep it above the bottom and below for the smaller net pots.