Kill la Kill - Image #826,794

Rainbow haired milf mode activated

That's actually common thing for art like this. We typically see the head as having a predetermined size no matter how it is interpreted (9 inches in height), as such the head becomes a means of determining a subject's height.

If the head becomes smaller, your entire view of the scale of the subject changes, and the whole looks greater. That's why the Hulk's muscles really get the feel of being massive, his smaller head throws you off.

In the case of pieces like these, the smaller head is to emphasize the shape of attracted regions.