In this comment we discuss some aspects of Phys. Chem. Chem. Phys., 2022, 24, 15851, by Allison et al., an article intensely motivated by our study of grazing incidence fast atom diffraction (GIFAD) for He-KCl(001) [G. A. Bocan, H. Breiss, S. Szilasi, A. Momeni, M. E. Staicu Casagrande, M. S. Gravielle, E. A. Sánchez and H. Khemliche, Phys. Rev. Lett., 2020, 125, 096101; G. A. Bocan, H. Breiss, S. Szilasi, A. Momeni, M. E. Staicu Casagrande, E. A. Sánchez, M. S. Gravielle and H. Khemliche, Phys. Rev. B, 2021, 104, 235401]. In particular, (a) we show that, contrary to first order perturbation prediction, the surface corrugation is not proportional to the tangent of the rainbow angle and, (b) we analyze whether a Morse-like formula, like the one Allison et al. use, is able to reproduce the atom-surface potential derived from density functional theory (DFT) calculations. In addition, we give some clarifications regarding specific remarks the authors made about our articles.