The effect of concentration of particulates on electromagnetic and gravitational forces applied to polydisperse mixtures is considered. It is shown that hydrodynamic properties, density, and susceptibility differences, and hence the related forces, are concentration dependent. Examples of particle trajectories flowing across a magnetized wire illustrate the role of concentration as regards flow patterns and capture probabilities. Higher concentration is associated with increased hindrance to deflection of particulates towards the wire, i.e., particles tend to follow streamlines of the fluid. Flow of polydisperse mixtures is dependent not only on concentration but also on particle size, density, and susceptibility distributions. In this context the relevant equations, related to constant and variable force field, are derived and their physical significance discussed.