You know only you can take the photo needed. You have to have the camera in very close setting then hold it to the light so it looks like the person seeing the coin is traveling across the surface. In my experience a person can see if the silver is on top or the encrustation. Now if this was a surface encrustation that was scrapped off the silver might look higher and the damage was rooted in the coin, but we'd see more of a pitting there. So I think there is a photo to be had to give us a better view. You can see below I can't pull that resolution out or the correct angle from your photo. Also, a later coin a person can make a case for the acid wash they did on the mixture before the strike so the spongy noble silver does look plated after the strike, but this is early enough the center should not be red like later coins would have and still be ancient. New photo please?