The matter of the ascent of Malchut to the place of the Eynaim (eyes) is called Yesod de Nukva. This is because Nukva means deficiency, where diminution is considered a lack. Because it is in the Eynaim, which is Hochma, it is nevertheless called Behina Aleph of the four Behinot. However, when the lower Hey is in Keter, and Keter is a desire to bestow, no diminution applies there, since there is no limitation on the will to bestow. This is why it is called Yesod de Dechura.