Do DWC Roots need airspace?

I have a DWC setup with 4 single 3.2g buckets and 8" net pots (Should have got the smaller one.) I can put one gallon of water in the bucket and there is about a 1/2 off airspace from the bottom of the net pot to the water level. Each site has its own airstone. Does there need to be an air space for the roots to breath or can they be completely submerged?

The general consensus out there is to leave about 1" below the bottom of the net pot. It works for me!!

i leave an inch or two. my buddy puts water right up to the bottom of his net pots but i don't suggest that

if your buckets only hold a small amount of water, then you're gonna have ph drift problems.