Evolution of the main-event shock flanks along two radial directions in the solar equatorial plane. The blue symbols represent the line at 0°, aligned with the positive x-axis in Fig. 4, while the green symbols represent a line rotated 135° anti-clockwise from the positive x-axis. The panels present: (a) hours elapsed since the blast wave injection, including power-law fits and observed spacecraft shock crossing times; (b) shock speed; (c) upstream solar wind speed; (d) upstream solar wind density, scaled with r²; (e) upstream fast-magnetosonic speed; and (f) fast-magnetosonic Mach number (M_fms).