I think Cox is scheduled to play for the England Lions on Friday (if he's recovered from injury), so he'll miss the next round of matches too (Glamorgan away, Middlesex home).
Somerset have been more astute with their overseas players and sadly Amir is a shadow of what he was the last time he played for Essex (I hope I'm proved wrong). Having white ball only players: Smeed, Kohler-Kadmore, also makes a big difference. Essex just look tired, uninspired and low on confidence.
I still wouldn't put it past them to put some wins together though.