You and Agustino are NEVER going to settle this business of transubstantiation.
For one thing, Agustino is calling it a "mystical" experience. It might be 1% - 3% clearer, maybe not, if he called it a "mystery" instead of a mystical event. People are thought to have "mystical experiences". Contemplatives work at achieving mystical experiences. A few people are struck by mystical experiences, usually to their dismay. Transubstantiation isn't something that one can achieve, work at, improve, or make happen. Through great effort, one can not improve one's understanding of a MYSTERY either. Mysteries are unfathomable and that's that.
The priest utters the incantation (the words of institution) and that's it from our end. HOW transubstantiation occurs is a mystery of the action of God [IF one believes that such a thing happens. Of course, if one doesn't believe that anything happens, then the whole thing is just so much hocus pocus].
No one has ever had a sensory experience that would tell them that the bread and wine had become, by a mysterious act of God, to be "the body and blood of Christ". I don't think there is any reason to think that the alleged author of the incantation, JC himself, was turning the bread and wine of the passover meal into his blood and flesh either.
If Jesus did say such a thing, my guess is that he was referencing a more ancient solemnity when the priest poured out the blood of an animal sacrifice before the people, to ritualistically 'seal' a covenant.
Jesus might not have spoken the incantation (Gasp! Heresy! Burn him
slowly at the stake!) The incantation may have been devised by the early church, as might the last meal of Jesus with the disciples. I'll assume here that Jesus did say it, though. We'll never know for sure, either way.
There is nothing to argue for in a Mystery. It's there, we do not, can not, have not, and never will understand it.
Myself, I don't like the whole business of mysteries, incantations, mystical bodies, and so on and I don't believe in them. What one REALLY has to strive to believe in is that the Church DID NOT cook up theories which were, shall we say,
implausible? and then called them a Mystery or a Mystic crystal revelation, or something, and then told the laity to just believe it or go to hell.