Initial dust-to-gas ratio required for growing dust grains to reach a relative decoupling radius R_dec = 0.01 (left) and 0.1 (right) for a scale height of 0.1 times the local radius. The ranges for p and q values corresponding to the values we have obtained in the radiative transfer calculations are delimited by the dashed lines (see Fig. 1). Dust-to-gas ratio between ≈0.01 and 0.03, and between ≈0.05 and 0.1 are sufficient for a grain starting at 100 AU to stop its migration at 1 and 10 AU, respectively.