Parameters of the ToI fit to the spatial distributions of galaxies with measured distances, that reside within 600 kpc of NGC 253. Shown are Δ_rms, the absolute rms plane height (far left); c/a, the minor-to-major axis ratio (middle left); i, the inclination of the best-fit plane with the line-of-sight (middle right); and d_NGC 253, the perpendicular offset of the best-fit plane from NGC 253 (far right). Blue shows the realisations drawing from the observed galaxy distances. They are more flattened than randomised samples drawn from isotropic distributions with identical radial distributions (shown in grey). However, they appear to be consistent with the parameters of satellite systems in the cosmological IllustrisTNG-100 simulation (shown in red). The mean and standard deviations of the shown distributions are given in each panel.