The ritual that Rhys had used was but a beginner's spell for those looking to pester their sires. Amadeus had much older, more powerful, ways of reaching out. It was far less likely to fail. In fact, if it did fail then the elder Tremere was going to start thinking someone was actively working to block Henry which would tell him a great many of things right there. Not all of them good. Rather none of them would be good if someone was blocking and managed to block him.
It wasn't overconfidence when you were as old as he was, as low of generation as he was, or as dedicated a study as he had been over the course of his years. All of which meant that if this did fail, Henry was lost to them anyway because of what it would mean.
Amadeus reached out his ring covered hand for the fledgling to take. An additional connection. An additional source of power as they both focused on it. "Just ask it to reach out and find Henry," he instructed. By it he meant the blood. The magic in it. It would do the rest.
If it couldn't find Henry because he wasn't there to be found, then they'd know it. The elder Tremere may have been joking about the E.T thing but in a way, they were doing just that. Just you know, in a darker blood magic way.