Normalized gas production (left panel) and exponent of the power-law model (right panel) are shown for models of spherical nucleus and 67P/C-G with a quasi-constant cross section. Gas production is calculated in Model B with growing layer thickness. The dust particle size is 10⁻³ m and the initial dust layer thickness is 2 × 10⁻³ m. The effective layer porosity is about 85%. The solid and dashed lines represent pre- and post-perihelion branches, respectively.