SiO (2–1)/(5–4) ratio as a function of T_kin and n(H₂) from the LVG modeling (grayscale). The panels show B1a and B0i cases. The observed line ratios (1.7 at B1a and 1.0 at B0i) are shown as a dashed curve, while the SiO (5–4) intensities (4.4 and 1.5 K km s^-1, for B1a and B0i, respectively) are represented by the solid lines. The line ratios plotted in gray are 0.16, 0.17 0.18, 0.2, 0.5, 1, 5, 10, 20 (some of them indicated with numbers).