I normally keep smaller fish in a tank that had lots of RFAs. Even now, I have a wild caught minnow from a local estuary in the 16g RFA breeding tank with over 30 RFAs. The minnow, only 1/2 to 3/4 of an inch long, has been fine for a couple of weeks now. I put 5 other minnows in my DT and they schooled which I thought was cool. But one by one they disappeared and there are only a couple small anemones in that tank. I assume other predators got them.
That said, a mandarin that tends to be a bottom dweller may be at higher risk to a big RFA.
That said, a mandarin that tends to be a bottom dweller may be at higher risk to a big RFA.