Principal English Translation: 

this locative suffix, typically used with place names, was long thought to refer to the "little" or "lower" version of another community, but Frances Karttunen suggests "New ____," saying it should be read as a spin-off community
Frances Karttunen, unpublished manuscript, used here with her permission.

Frances Karttunen: 

-TZINCO The honorific of postposition is formed by adding not simply –TZIN but –TZINCO. See TZIN-TLI, -C(O).
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 312.

Lockhart’s Nahuatl as Written: 

the reverential of relational words
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 240.

Attestations from sources in English: 

Here are some older ways of translating place names:
--teopantzinco = at the church (a reverential here?)
--atoyatzinco = at the little or lower Atoyac
--Xochimilco vs. Xochimiltzinco = the latter is "Little Xochimilco," with the -tzin- having the effect of a diminutive in this situation and distinguishing it from the larger, better known Xochimilco