Hi all, thank you for checking this website.
This article is on “Wing Shape” one of the shape to remember for better tile efficiency.
Please see “Wing Shape” hand below.
The shape of Pinzu: circles is called “Wing Shape”. This is called “wing” probably just because the shape is symmetric, but I’m not sure. Do you see what are the effective Pinzu tiles for Tenpai ? They are 25p, 69p, and 47p. Actually we don’t encounter this such often, but please recognize this as good shape to make 1 head and 2 Mentsu. Variation of this is 33445667. If you draw 23458, you can also make 1 head and 2 Mentsu.
I hope this will be of some help to you!