Abundance of N₂O, C₂N, C₃H, C₃H₂ and OCS relative to H₂ throughout a two-component O-rich outflow with different mass-loss rates Ṁ and clump volume filling factors f_vol. The characteristic size of the clumps at the stellar radius is l_* = 10¹³ cm. Blue lines: porosity length h_* = 2 × 10¹⁴ cm. Green lines: h_* = 5 × 10¹³ cm. Red lines: h_* = 2.5 × 10¹³ cm. Solid black line: calculated abundance for a smooth, uniform outflow. Solid coloured line: density contrast between the inter-clump and smooth outflow f_ic = 0.1. Dashed coloured line: f_ic = 0.3. Dotted coloured line: f_ic = 0.5. We note that the models with f_vol = 0.4 (red) have the same porosity length as the one-component outflows with f_vol = 0.2,  l_* = 5 × 10¹² cm and f_vol = 0.4,  l_* = 1 × 10¹³ cm. For reference, 1 R_* = 5 × 10¹³ cm.