Same as in Fig. 11, but showing the evolution of the H i column density between clumps N_HI,IC (= (1 – FF) × n_ICL, with L as the physical size of the shell), as a function of the total . When the temperature in and between clumps is the same (star and the circle dots), the high-contrast regime can be observed by applying an optically thick interclump medium for Lyα photons (i.e. from N_HI,IC > 6    ×    10¹³ cm² with b = 40 km s^-1). But, assuming a higher temperature between clumps than those of the clumps (square dots), the high-contrast regime disappears as the interclump medium becomes optically thick for Lyα photons (i.e. from N_HI,IC > 3 × 10¹⁴ cm² for T = 10⁶ K).