The integrated intensity diagram generated from the G11 observations of three SiO lines (J_up = 5, 6, 8), corrected for beam size and for filling factor effect: filling factor of 1, 0.5, and 0.2 in black, dark grey, and light grey squares. The result of our best-fit model for the H₂ and CO lines (n_H = 10⁴ cm^-3, b = 1.5, ν_s = 22 km s^-1, and an age of 3800 years) is shown with 1, 2, or 4% of the pre-shock Si placed in the grain mantles in red empty, dotted, or filled circles.