Which way does the pillow go? The larger part under the neck or the smaller part?

There are two support lobes, one 2.5”-3” and the other 3.5”-4.” 

The lower lobe is usually used under the neck and the higher one under the knee, but it also depends on your neck curvature and comfort and whether you lie on your back or side. 

Please find and use the most comfortable way for your personal needs.