Illustration of the topological configurations considered in previous studies. For each approach, we show the relative contributions of sectors each corresponding to a specific Cloudy model. These contributions are equivalent to the fraction of the total solid angle in 3D. The light blue shell corresponds to the ionized gas, the dark gray shell to the neutral gas, and the red arc to the photoionization front. In Cormier (2012) (a), the model used an H ii region connected with a PDR, with the PDR covering factor scaled a posteriori (cropped shell in white), and an additional model is considered a posteriori to account for the diffuse ionized gas. In Cormier et al. (2019) (b), two sectors are considered with the PDR associated only with the high-ionization parameter sector. In Polles et al. (2019) (c), models use a single sector with a varying depth. In Lambert-Huyghe et al. (2022) (d), observations are compared to a mix of pure H ii region and PDR components drawn from the same Cloudy radiation-bounded model. In Lebouteiller et al. (2017) (e), up to four sectors were considered with different depths.