The test of the WKB scale-separation conditions for PSR J1856−3754 (solid) and PSR J0720−3125 (dashed). (a) Comparison of λ = c/f with Δz and ﹩{r}_{{\rm{em}}}^{{\rm{KG}}}﹩. (b) Scale-separation measures λ/Δz and ﹩\lambda /{r}_{{\rm{em}}}^{{\rm{KG}}}﹩. (c) Adiabaticity measures k_emΔz and ﹩{k}_{{\rm{em}}}{r}_{{\rm{em}}}^{{\rm{KG}}}﹩. Across the MHz–GHz band, ﹩\lambda /{\rm{\Delta }}z,\lambda /{r}_{{\rm{em}}}^{{\rm{KG}}}\ll 1﹩ and ﹩{k}_{{\rm{em}}}{\rm{\Delta }}z,{k}_{{\rm{em}}}{r}_{{\rm{em}}}^{{\rm{KG}}}\gg 1﹩, satisfying the WKB ordering in Equation (A10)