I've been assuming that Jacob has had this all planned out from the get go. That he knew MiB's loophole and has already been starting a counter to make sure that MiB fails. And one of my basis for this theory was that he didn't fight back against Ben when he tried to kill him.
This has since changed for me. According to Miles, Jacob didn't want to die and he also hoped he was wrong about Ben. Which means even though he didn't care about Ben (because of Ben's lust for Power and prickness no doubt), he still wanted to give him the benefit of the doubt that he may become what he knows he can be.
Now Richard on the other hand said that he was a follower of Jacob and that he was told he had a purpose. And as a show of good faith (assumption) Jacob gave Richard a gift. He touched him, which we all know now grants you long life.
What I'm proposing now is this. What if Jacob didn't fight back against Ben, not because it was all a part of his place, but because he didn't think Ben yet deserved his gift. And to fight back would mean that he had to touch him?