OK, here goes:
I am new to brewing, but I am an experienced chemist. Considering the time, effort, and money that each batch represents, you/we should view every batch as an experiment. Control as many variables as you are able, learn as much as you possibly can; take detailed notes.
Probably, as I plan to do, you will have a stock 'house brew' for everyday 'use', and your other batches will be experimental. In each case, you want to get out of a batch at least as much as you put into it. Errors are bad, but errors whose causes are unknown are MUCH worse..
Re: Headspace; Oxygen is 23% of the atmosphere/headspace, and when it is present, yeast grow aerobically: they prefer to eat alcohol and make vinegar.
Enough theory: Either use a vessel of appropriate size(losing liquid to foam is better than losing flavor in an entire batch), or try this in an emergency: cleanse a thin poly bag both sides and stuff it into the vessel(opening to stay outside the vessel! yes, like a bladder), inflate it with clean, filtered air until it fills the headspace. I'm not saying the bag is not permeable to oxygen, but at least you have SOME barrier until the yeasties can generate a CO2 blanket. Yes, you have to watch it. Good luck.