Realistically speaking, isn't it situational?
What if I am going in and out of consciousness on the ground, having trouble thinking, and then an ASE priest shows up and says "Yes, Mstislav, the Theanthropos is the union of two prosopa"? Or an OO priest schooled in the beliefs of Severus of Antioch arrives, proposes the Eucharist and says "we must confess the union of two hypostases"?
I really don't know, because even among priests there are those with different beliefs. Some of them, like the RCs and traditional Protestants actually agree with the EO position on the main questions about who God and Christ themselves are, like some Catholics agreeing on the substance of the issue of the filioque. I don't see St. Augustine's belief on original sin to be so drastically different that it demands schism, since he is still a saint in our church too.