"God, for Augustine, is fundamentally intelligible, i.e., accessible to the mind. He is to be identified with the Plotinian level of universal mind, or Nous. But among the Neo-platonists of the Christian Greek world, God is beyond Nous. He is to be identified only with the transcendent One. In Dionysius the Areopagite...the level of Nous corresponds to the created angelic realm. Augustine, committed to the intelligibility of God, dispenses with the Plotinian One. For him the ultimate divine level is Nous. But Dionysius and his Greek successors conceive of God as transcending Nous, and therefore as being in his essence inaccessible to the human mind."
Fellow Workers with God: Orthodox Thinking on Theosis, Norman Russell, 118.
Ah, that explains a lot.