I guess this is where style plays a big part in the determination. Compare yours with: Trier - https://www.acsearch.info/search.html?id=35503 Cyzicus, but with the KS in exergue - https://www.acsearch.info/search.html?id=791032 Mine again, with the PTR, and KS above - The mentioned hoard finds probably helped confirm the thinking that these were struck at Cyzicus.
The handsome follis pictured below was recently auctioned by Roma Numismatics. My bid on this coin was steamrolled quickly, it sold for over $1,000.00 ! I like the action scene on the reverse . Severus II as Augustus, Aquileia Mint, AD 306 - 7. AE follis: 10.04 gm, 27 mm, 12 h. RIC 81b.
Dear Warren, the helmeted Diocletian follis is fantastic. I think it is a particularly appealing and forceful portrait for this scarce variety. Here is my most favorite Diocletian from my collection. I just love the abdication series. The coin is not rare, but in practically perfect condition. It has a certain medallic quality to it. I think this series does not have to shy away from comparison with 1st century sestercii
... here is another abdication follis from my collection. The exemplar above is from Trier (Germany), this one was minted at Alexandria (Egypt). Totally different style:
I also like the portrait of Galerius on this follis a lot. On this exemplar his moustache is clearly visible.
I know, this is about portraits, but I bought this standard Diocletian for the particularly fine reverse:
Back to portraits ... this military portrait of Constantius I is very attractive, even if it is not particularly rare like the variety with helmet.
Another Constantius I, with a nice expressive portrait. I picked this one up on Ebay just a few days ago, for a very reasonable price.
This Maximianus follis is attractive, because it has not so much as a hint of weakness. A perfect strike with no wear.