In a course of a Twitter conversation, I twittered to(ward) Evirus: "Remember how Ritsuko demonstrated the greeting hand, and 3 inept idols (inc. Iori) tried to do it", and he replied: "Actually...I don't." Very well, here's the scene from IM@S TV 18:

In order to acquire the screencap, I rewatched the episode, and perhaps unsurprisingly, the scene is nothing like what I remember. In my recollection, it was vividly obvious that Ritsuko was better at the basics of idol-ing than Iori. But on the rewatch, the difference is not all that striking, and it's not in hands; the biggest difference is that Iori stoops when she extends her hands. Art is typically horrible and even has low-res zoom later in the episode, in our day and age. I knew it even back then, but I guess I was spellbound and saw what the anime implied, not what it actually presented. At one time we should see Ritsuko's hands up close, but the back of Iori's head completely obscures them! It's implied that we see them, but it was too hard for A-1 to draw.

UPDATE: There was a small discussion in regards to kamehameha. In known canon, nothing stops a Ki user to form the ball wherever, such as at a tip of a finger. So Ritsuko's move could be just as effective, but it feels wrong anyhow. We are not used to control things at the outside of a hand.