What determines levitation height?

A combination of particle density and magnetic properties, Levitation Agent concentration, media density and instrument magnet configuration determine the final levition of a particle.

Particles start off randomly distributed in the fluidic channel, and reach their final levitation height in a size-dependent amount of time. 

Large objects reach their equilibrium height faster than small objects, such as debris.

Thus larger objects can be separated from smaller objects and vice-versa by adjusting the levitation time, if the levitation time is shorter only the large particles will move into the final levitation height and can be isolated from the smaller objects.