Help With Mint Mark- Constantius Gallus Ae2 Fallen Horseman

I received this coin in an uncleaned lot, and since I like the look of it now, I'd prefer to leave it as is with no cleaning while getting as precise an ID as possible. It's only the second coin I've tried identifying myself, so I apologize if this is very basic for the more experienced folks on the board.

Constantius Gallus AE2
351-352 AD
Fallen Horseman, Phrygian Helmet
Weight/Size 4.0g/21mm
Mint ?

I've pondered the Mint for several days, but am leaning toward Rome based on the following clues. Any help would be great. Thanks!

- I think in the exergue it could be R wreath S, but the first and last characters are very unclear. It might match RIC VIII 261 on wildwinds, although that is listed as AE3.

- The DNFLCL in the obverse legend marks it as definitely Gallus, and I believe the Gamma in Reverse field narrows it to Rome, Cyzicus, Nikomedia, or Constantinople.


- Obverse field is unclear, but has what could be a 'B' or an 'A' or a funky Delta behind the head. 'B' (and maybe 'A') indicates Rome, but a funky Delta, or some other character doesn't help deduce anything new.

Thanks again.