A classic downward facing dog (adho mukha svanasana) looks like a pyramid.
In order to get a stretch for the shoulders and upper back one can move the head to the floor. To squeeze the shoulder blades supports the process.
I start with a dynamic phase and swing the upper body in direction to the legs. The head gets closer to the floor. After 12 times I stay in the position and try to get even a bit deeper.
This looks not very dramatic when I’m doing it.
That’s why I do these exercises.