I believe the twins fed off each other with each becoming stronger knowing that his "Twin" had his back. Now that the are separated and don't have each others support, they move to another level. Testa isn't so tough any more , but Senter still is a true hardass. Sounds like Persico recognized this and uses him as his muscle. With Testa acting cowardly in the incident described above, I bet the word spread fast through the prison system that he is a punk