At the bottom of the main stalk at the point roots start. This forms a kind of ball of roots. This area of roots needs more air than water. If it stays wet toooooo long the plant starts to drown. Outside it can rain for 3 days, but much longer and problems start. Same with hydro. That's why with a constant feed you need to keep it over to the side of the airball. The rootball needs at least one hour of oxy to be good in a 24 hour period.

All other roots that hang down can stay under water 24/7.

Either way will work. Tweaking things for yourself is what it's all about. find a path, stick to it, tweak to change. This way it is much easier to look back and make tweaks or see what the tweak did.