Not sure I'm the right person to answer. I don't have Chromis. In my tank I have 2 average size clowns. 2 inches each, 1 big banded coral shrimp with whiskers extending to 1/3 of a tank, about 10 turbo snails, 2 emerald crabs, some zoas, 1 anemone, I think that Clowns can beat up quite a few fishes. When I added the second Clown they were beating each other for a couple of days but now it's peace and friendship.
My tank is only 8 gallons so likely will not be adding any more fish. Clowns will definitely start beating Chromis up. Generally Clowns are pretty peaceful and get bored fighting so question is when and if they stop.
By the way, what happened to the Nano sub forum...? no paging is available and only new threads coming up