Notice how in "Faith", as soon as Kara's Leoben is on the basestar again, on his home territory - or even before, when he was sitting on the raptor behind Kara - he's suddenly...serene. Calm and very, very still. He becomes the rational, deliberate basestar!Leoben that we see in the Cylon-only scenes. None of his sudden, unexpected veering turns in tone and mien; no longer the Leoben who speaks truths mixed with lies, who plays mind games and tries to manipulate the emotions of the humans to his advantage.
I find the change in his presentation fascinating, because I think lots of people had previously noticed the contrast between Leoben when he is with Kara and Leoben when he is talking with fellow Cylons, and assumed that they were different copies of the Two model. They even dress differently.
"Faith", however, tells us that ALL the Leobens are obsessed with Kara, and ALL the Leobens can presumably present both those faces, and switch back and forth between them: the volatile, passionate, weirdly seductive/repulsive face he puts on when he is among the humans, and which he uses when he is trying to "help Kara realise her destiny"; and the far more stable, but still intense, Leoben that he becomes when he is among his own kind. Leoben on the basestar NEVER CRACKS A SMILE. Of course, the other Cylons who have lived mostly on the basestars and spent little time developing an individual identity are also quite basic and machine-like in their emotional range. But the Leoben in "Faith" was just last episode showing expressions of elation and sadness and desperation on the Demetrius. And then the moment his task was accomplished, and Kara had found the basestar, it was like he became a different person; still genuine, still human somehow, but not the same. So is one of those faces an act? Or both of them?