Comparison of spiral arm properties between our two models for HD 163296. Top: primary and secondary spiral arm contrast with respect to the disk background. We find that the locally isothermal model shows consistently higher contrast. Bottom: pitch angle of spirals as a function of radius. Because the two models have identical aspect ratios, the overlap of the two curves is to be expected. The vertical black line marks the planet location. The dotted black line corresponds to the analytical formulae in Rafikov (2002), Eq. (44), and Muto et al. (2012), Eq. (1).