I think alot of it has to do with footwork. Cro Cop has fought in the ring for years in both K-1 and Pride. He mastered the art of closing off parts of the ring, backing people up into corners etc. Also, without the cage to lean up against, in order to engage a clinch, his opponents have to move out of the way and usually they moved right into a CC head kick or left hook.
^ Pretty much this. I'd say this plays a big part in most of his UFC losses, except for Kongo who was just physically too much for him. And CroCop has become slow in the last years.