Exponent of the power function approximating the total gas production of 67P/C-G, 81P/Wild 2, and 103P/Hartley 2 (from top to bottom) as a function of the heliocentric distance. The left and right columns depict the results with a dust layer composed of particles of size 10⁻⁴ m and 10⁻⁶ m, respectively. The corresponding layer thicknesses for these two particle sizes are provided in Table 2. The dash-dotted lines depict the power-law exponents obtained for different models utilized before and are explained in the text. The exponents of different models for 67P/C-G are shown, and corresponding values are shown in the text.