Numerical diagnostic of contamination of the high-resolution zoom regions in TNG-Cluster by lower resolution mass elements, at z = 0. Top: Minimum distance to the closest low-resolution dark matter particle from the center of each halo (red markers, dashed line), and the distance at which the low-resolution particle fraction exceeds one per thousand (blue markers, solid line). Bottom: Histograms of the number of halos with given minimum contamination radii, as measured by the single closest low-resolution dark matter particle (red) or as when the low-resolution particle fraction exceeds 10⁻³ (blue). A handful of halos have one or a few interloping low-resolution particles within one or two virial radii. However, the median distance out to which halos are more or less fully resolved by high-resolution particles is ∼4 − 8 virial radii (≳5 − 10 pMpc).