...you need to read this post. Seriously.
I have never, outside of RyuTe, been shown how to punch this way. The only thing that has come even remotely close is Kiyoshi Arakaki's instructions in The Secrets of Okinawan Karate: Essence and Techniques. Everybody, everywhere, starts out with "make a tight fist."
Interestingly, Arakaki says that Nagamine Shoshin showed him how to punch very similarly to this (though not identically), but in Nagamine's book, he tells the student, "Make a tight fist."
And you don't think some teachers hold back crucial information?