The idea that the humanity and divinity are in communion doesn't seem to us to express the natural union which we understand to have taken place.
It must be remembered that Nestorius believed the Tome of Leo expressed his Christology. This certainly doesn't mean that Leo had a Nestorian Christology, but it would seem to indicate that far from being the last word on Christology which Leo thought his Tome should be, in fact it contained too much ambiguous language which failed to exclude a Nestorian interpretation.
The second passage is also problematic since Theodore, Theodoret, Nestorius and Ibas would all agree that there is in Christ one Person of God and man. But there understanding was fundamentally flawed. They were unable to say that Christ was the Word of God and that the Person of Christ was the same Person of the Word.
Alpo is not happy with the idea that there is only one subject in Christ who is the Word, and I am not going to leap on him, but I do think that there is more than enough Eastern Orthodox conciliar evidence to show that Eastern Orthodox does not allow it to be said that there are two subjects or two persons in Christ.
If the Word of God is not the subject of the humanity then there is some other subject, and if there is some other subject then it was not God the Word who died on the cross for our salvation.