I should add two items:
Schlosser, Marianne, Cognitio et amor: Zum kognitiven und voluntativern Grund der Gotteserfahrung nach Bonaventura, Münchener Universitäts-Schriften, Veröffentlichungen des Grabmann-Instituts zur Erforschung der mittelalterlichen Theologie und Philosophie, 35 (Paderborn: Schöningh, 1990), though this is later than the 12thc, Schlosser includes good review of literature and provides a guide to Bonaventure texts on the topic
David Balás, O.Cist., Metousia Theou: Man's Participation in God's Perfections according to St. Gregory of Nyssa, Studia Anselmiana, 55 (Rome: Herder, 1966) deals with one of the most important Greek sources for the image of God theology and would be useful to put the Augustinian tradition into context. At the Cistercian Abbey in Dallas you have access also to Fr. Roch Kereszty who is extremely knowledgeable on the Cistercian tradition in this regard, as is Fr. Denis Farkasfalvy, even though his speciality is New Testament. If I am not mistaken, David Balas is a member of the same community, though I do not know if he is still active.