Dust/gas radial velocity ratio, υ_r/u_r, as given by Eq. (12) as a function of radial distance from the star. The validity of the curve extends to the location of the snow line (2–15 au, depending on the stellar accretion rate for the assumed α = 10⁻⁴; see Batygin & Morbidelli 2022), where S_t (and hence υ_r/u_r) jumps by a factor equal to the square of the ratio of fragmentation velocity thresholds for icy and rocky particles.