Assessing the model (36) used by Hamilton et al. (2024) for the same parameters as used by these authors. Plotted as function of radius from top to bottom, I show the relative perturbation strength of the forces, the relative amplitude A_m = 2 of the density perturbation (assuming the unperturbed disc is maximal with scale radius related to the co-rotation radius of the spiral as R_cr = 1.5R_d), the phase offset between the potential and density, and the density pitch angle.