Perspective, converging lines, and vanishing points must be eliminated in flat space. Planes must be frontal, not longitudinal. The frontal plane emphasizes the two-dimensionality of the screen surface. The diagram reveals the frontal surfaces in the photograph. There are no longitudinal surfaces and the vanishing points have been eliminated.
For aerial diffusion to be an effective depth cue, there must be an object unaffected by the aerial diffusion and another object affected by the aerial diffusion in the same shot. The comparison between the two objects creates depth. In this shot the actor is walking outside on a snowing day, particles of snow falling. this creates depth along the road and her walking the direction.
Normally, objects with more textural detail appear closer. If BG objects are given more textural detail, they tend to move forward or advance into the FG. FG objects that lack textural detail will tend to recede into the BG.