I'm an outsider in this discussion, so pardon any naive remarks.  I was under the impression, though, from something I read somewhere (that statement wouldn't get past Wikipedia) that Cīna in Tantrika texts, especially the Mahācīnācāratantra, referred to what we today call the Assam-Burma region.  Meghalaya, Manipur, Nagaland, Tripura, Northern Burma that sort of area.

Best,

Dominik