The hanging legs of the disappearing Christ

In the promotional leaflet of a certain publisher, I spotted the following:

I think it comes from Isabella of Castile's Book of Hours.

It seemed a little odd, this image of Christ during the Ascension, his upper body covered with a cloud, only his legs visible. More often, he is depicted with his full body in sight.

Then I remembered that I had read about this kind of iconography before. Apparently, it originated in eleventh-century England, and its motivation lies in biblical exegesis. They wanted to emphasize the idea that Christ ascended to heaven by his own means. Were he to be represented standing in the cloud, or enthroned in a mandorla carried away by angels, the misleading impression could be given that he needed some external help. Hence the hanging legs!

Here's an earlier example. The classic study of this iconography is Meyer Schapiro's "The Image of the Disappearing Christ: The Ascension in English Art around the Year 1000".