Penisini's poor form is only in his defense, not his attack which hasnt dropped. That could easily be put down to the new defensive structure and style that Ryles has introduced. Add to the fact he has shifted sides which means a change to angles, shoulder to use, line speed on that edge and he has new partners to build trust in and work on timings with. His running metres, LBs and TAs are all on par with previous years.
So, lots of reasons that don't rely on him being dirty because he got shifted to a new position and his brother isn't playing with him.