Is the cutoff radius in DPD simulations with a fluid of constant density arbitrary?

The DPD (Dissipative Particle Dynamics) method was used to simulate the flow of a fluid occupying the space inside a rotating infinite long cylinder. The fluid was initially at rest and rigid body rotation was expected to be reached. However, as the simulation proceeded, the DPʼs (Dissipative Particles) began accumulating near the wall, leaving the cylinderʼs core empty of DPʼs, obviously, an aphysical solution. To solve this problem it was suggested to set the cutoff radius as a function of the DPʼs number density. A conceptual explanation is suggested.