The Armenian Church developed its dogmatic, liturgical and ecclesiological peculiarities through centuries of confrontation, dialogue, and contrast with the "other". A crucial step in this process has been the shift from an Antiochene-oriented (or Edessa-oriented) theological influence to a more marked Alexandrian-Constantinopolitan position, which occurred in the aftermath of the council of Ephesus, in 431. Although this historical development has been largely disentangled thanks to the works of Nina Garsoïan and Gabriele Winkler, there are still details that remain blurred. One of these is the letter addressed by the Armenian patriarch Sahak I (d. 438) to Proclus of Constantinople, around 435-436. The letter is at the center of an intricate conundrum that involves philological, historical, and Christological issues, all related to how Sahak - or Pseudo-Sahak - viewed the Armenian Church in relation (or in contrast) with Constantinople, Persia, and Antioch. Admittedly it is still not possible to see a definitive solution to the issues posed by the letter, as attested by the fact that the two scholars mentioned above, Garsoïan and Winkler, remained with two opposite views on the subject. Nevertheless, this paper aims to bring the topic to the fore, and to propose methodological approaches for finding a way out of the conundrum.