Try Auslogics to see if that will help with the fragmented files there. Despite any number of attempts however certain files found fragmented will stay fragmented while not effecting anything else on the drive.
The only way to deal with files themselves that can't be defragged is to remove them if unable to replace them with unfragmented versions of the same. I'm sure you don't want to rush to delete any files there. First you will want to find out which files are highly fragmented there for either resaving projects, fresh downloads, etc.