The standard work on atria, posas and open chapels is still John McAndrew's book "Open Air Churches of Sixteenth-Century Mexico." While the European and Muslim traditions are a possibility, evidence seems to point elsewhere, as I recall. The Mexica, in particular, and the Nahua, in general, also had enclosures around their temples to designate sacred space. The utility of the arrangement was best exemplified by Diego de Valades in his "Rhetorica christiana."
John F. Schwaller
University at Albany