What is interesting is that the different mints show different barbarians. Constantinople and Antiochia seem to show a Parthian (as indicated by the decorated trousers). The mints from Thessalonika clearly shows a Germanic warrior, so does probably the mint of Alexandria. The nationality of the barbarian on the coin from Aquilea may be indicated by the strange head, but I don't know who this stands for.
Your Aquileia coin shows a Phrygian cap as seems to be the norm on these seated captive issues. You do get different coins with bare heads and caps from the different mints and if you really want to be into it some are depicted bearded and other beardless..... On my two Constantinople coins above you can see that one is bare headed and the other wears the cap. The bare headed coin shows long braided hair and a beard but the Cyzicus coin shows a tighter cut head of hard but still seems to illustrate a beard. Below is an example of a cap but no beard... The number of combinations is huge
The following coin is worn, but I noticed that the head of the horse does not touch the ground. Somewhat unusual for that wide series of coins FH.