B,
Only two C. Cox's on the Medal Roll for the campaign; both Privates one in the 4th (King's Own) Regiment & the other in the 60th (King's Royal Rifle Corps) Rifles.
It is possible he was in the employ of the Union Steamship Company the owners of the Asiatic.
I have an engraving of the 99th embarking for the campaign, I'll have to check the ship that they are shown boarding.
Isandlwana