When first starting off with clones before roots have emerged from the net pot then you might want the level just touching the bottom of the net pot but or general use an inch below is where it's kept so the pot itself isn't always soaked. The popping bubbles from the airstones keeps everything nice and wet.
Once there are lots of roots in the water the ones in the net pots don't even absorb nutes and are basically pipelines for the water etc to get up to the plant. The fine root hairs are where all the action is for sucking up water and food and that's why root rot can kill plants so fast as those fine hairs get killed off first and the plant dies of thirst while sitting in a tub of water.
You should put a link to your grow in your signature if you want people to find it like I do with mine. I mainly keep a bit of a journal so I can keep track of what I'm doing and have a record of dates when I finally did something.
I'll be getting back into DWC full time in September once I get back from a month or more in BC. Leaving around the end of this month. I'll be starting up a new grow journal then for that.