Head space doesn't matter in primary. Many use an open bucket. The primary fermentation gives off enough co2 to protect the must. Those active yeast need some oxygen anyways.
Reality is an illusion that occurs due to the lack of alcohol.
Give a man a beer, he'll drink for the day.Teach a man to brew, he'll be drunk the rest of his life.
I have 8 carboys, 8 cornies, 5-1 gal jugs, 200 wine bottles, 10 cases of beer bottles and a nice assortment of flip tops....My goal is to keep them at least 50% occupied