Same as in the bottom panel of Figure 3. Compared to the fiducial run (top left), we either halved the integration timestep (top right); halved the softening length (bottom left); or doubled the sizes of the Cartesian, radial, and azimuthal grids (bottom right). In all cases, the measurements of the local relaxation rate are fully consistent with one another. Here, the use of the Kuzmin softening kernel (Appendix G) is instrumental to obtain consistent results over a wide range of softening lengths (see Section 4.3).