Model predictions (Sect. 2.3) compared to the location of the ISM filaments in the M–L phase space (see also Fig. 1). For simplicity, we display only those molecular filaments. Using Eq. (10), different lines indicate the expected normalization values for characteristic filamentary (A = 30, 10, and 3; black lines) and prolate spheroids (A < 3, orange shaded area) geometries. We added also the typical A observed for HFS (A ≤ 1.5; orange dashed line; e.g., Kumar et al. 2020). We also indicate their corresponding surface densities according to Eq. (11) in the legend.