Right! There were no coinage in other metals at that time in China. At least, not for regular currency.
My unscientific reply is that it has to be FTR types. I have about 900 coins and they represent almost 10 percent of the collection. Gloria excertitus would have to be a close second.
Here is another very common type: 14 mm. Constantius II, struck 347-348, just before the FEL TEMP REPARATIO reform of 348 and after, Kent thought, a gap of six years without the production of AE coins. This one is from Antioch: SMANTI, RIC VIII Antioch 113. The type is "C4" and from fifteen (15!) officina. Fifteen officina can produce a lot of coins (and that's not counting the other mints). This example has the gorgeous (natural, not recent) "desert patina" or, as I call it, "black and tan patina" so often seen on coins from that part of Syria.
Cast bronze are a bit less common. The astragalo / shell are not too hard to find and can be had for about $100 plus or minus a bit. I have not seen any that have great details.
When I still bought uncleaned lots, "Soldiers with Standards" were always my most common. This particular one is not one of the more common examples nor was it from an uncleaned lot but is my best(not that I have too many): Roman Empire, Constans as Caesar Æ3, 333-335 AD, Trier mint. FL IVL CONSTANS NOB CAES, Laureate, draped and cuirassed bust right / GLORIA EXERCITVS, Two helmeted soldiers standing with spears & shields, facing two standards with a palm branch between them. In exergue, TRS. RIC VII Trier 560(R3)