Answer: Bina operates until its middle under the influence of Keter, and from its middle onward it wants to resemble Keter, so it develops everything by itself.
It receives the attributes to bestow from Keter and in order to implement them and to resemble Keter, it begins to bestow unto the lower, just like Keter.
Because nine Sefirot descend from Keter, the first nine letters develop from Bina, (nine Sefirot the last part of Bina).
The next nine Sefirot belong to Zeir Anpin.
The last four letters, Kof, Resh, Shin, and Taf belong to Malchut. All together there are 22 letters, 22 forms of bestowal of the upper force unto Malchut.
In Malchut there are five additional letters. These are special letters of the 22 letters which create their final forms in Malchut. All together there are 27 letters of the alphabet.
From the Kabbalah Lesson in Russian 3/5/17