Envelope mass as a function of time for initial conditions as in run IIa in Rogers et al. (2011). The thick dotted line is the result of Rogers et al. (2011) obtained in a combined grain evolution and core accretion simulation. The blue lines are our results for different values of the grain opacity reduction factor. The lines are f_opa = 0.02 (solid), 0.003 (dotted), 0.001 (dashed) and 0 (dot-dashed).