Your diaphragm works like a jellyfish when it's in the water. In the sand it doesn't work anymore. It rests on the abdominal viscera that give it its shape. The following pictures show you a particular behaviour according to the diaphragmatic contraction.

Presentation with this short film of the digitation orientations for a thick and flat chest.
It is important to observe the orientations of the syringes and pumps in profile. Associated with an inspiratory delivery above the umbilical and an expiratory withdrawal below the umbilical for the thick thorax.
Then an inspiratory delivery under umbilical and an expiratory withdrawal under umbilical for a flat chest.