What Rex said , just check the ph, temp ,ect. The tds could concentrate the nutrients if running too low on water but two inches is fine ! Some run 1/2” below the net pot . When they get larger and use 1/2 gallon+ a day I’ll put it within 1/2” of the net pot .A watcher eh?
I think as long as the roots are touching and your within parameters (ph, temp, EC, etc.) then it's OK.
The biggest thing is to not go past a week without a change.
The others you tagged should be able to give you some better advice, as its Slightly different with my external reservoir.
Hope that helps! Even though I feel like I didn't really answer your questions