Since particles tend to follow a straight path, films deposited by physical means are commonly directional, rather than conformal.

Larger particles tend to drop out of the air quickly and also are expelled from the lungs by coughing and other defenses.

Fine particles tend to stick to each other, and hence the sieving process is not an effective method.

Bigger particles tend to sediment faster and thus have higher svedberg values.

In case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area.

As such, only particles with high KE will tend to be moving up.

These particles tend to be the ones that transfer energy: photons, gravitons, pions, etc.

Once a magnetic field has been created, electrically charged particles tend to spiral around its field lines and slide along them.

So over time, the small particles tend to head downward and the large particles upward.

Thus, larger particles tend to become sorted to the top of such a mixture.