I tried to find Prof. Ehling's JNG article online (thanks for the reference), but it does not seem to be available.
While searching, I did gather that the only reference to an Armenian war comes from Eusebius, and is tied to an account of a horrific famine and plague that Eusebius has ravaging the eastern empire after the war, which Eusebius then echos in the demise of Daia due to starvation after his defeat by Licinius.
One might have thought that such divine retribution of famine and plague against Daia would also have been at least mentioned by Lactantius in his "On the death of the persecutors", but there is no mention of anything related other than mention of a food shortage caused by Daia's stockpiling (for his army?), which it seems may well be the only factual basis for Eusebius fantastical account of not just a famine but a plague as well!
There is a very enlightening discussion of this Eusebian account (from his Historia ecclesiastica) in this article "The Famine and Plague of Maximinus (311 to 312)" by Kennedy & DeVore.
https://muse.jhu.edu/article/885031/pdfWhat this article appears to successfully show is that this account, and maybe by extension much of Eusebis' writing, is at least as much rhetorical as historical in nature, specifically following the rhetorical approach of the greek historian Thucydides, which allows and encourages wholesale fabrication of detail as long at it supports one's rhetorical goals!
I have to assume that Lactantius, also being an educated man, would have read Thucydides, and certainly been familiar with the contemporary norms of what could pass as "history" (or however such writing was regarded). Some of Daia's writing such as that of Galerius' putrefying private parts seems to come from the exact same school of rhetoric and "ekphrasis".
Anyway, given that Eusebius seems to have reimagined a localized food shortage as a regional famine and plague(!), it does rather bring to question what was the factual basis for Daia's Armenian war! I suppose there must have been something to base it on, but maybe a minor conflict rather than a major one, especially given that Eusebius is the sole source.