Three Metaphysical Compositions (a hint)

Here is the riddle, again. In what sense that makes them all "metaphysical compositions" are the following three paintings alike?

David Hockney's "Going up Garrowby Hill", 2000.

Giorgio de Chirico's "Metaphysical Composition (Composizione metafisica)", 1914.

Diego Velazquez's "Las Meninas", 1656.

Jay has noted an important clue: "we're looking from the eyes of Velazquez as he paints his own reflection in a wall-sized mirror".

Here's another hint. Of "A Closer Grand Canyon", Hockney, I think, has said, "This is not a picture of the Grand Canyon. It is a picture of looking at the Grand Canyon."