Extracted results from output data elucidating the formation process of ear-like structures. Panels (a)–(d): temporal evolution of the forward shock with different γ_eff, where RX curves represent the averaged shock radius with a specific azimuthal angle X(0,45,90 deg; with regard to the r-axis). Panel (e): azimuthal distribution of the forward shock radius at 1000 years with different γ_eff. Panel (f): derivative of shock radius with respect to the azimuthal angle at 1000 years with different γ_eff, with its absolute value being plotted. Panel (g): relative positions of contact discontinuity (the ratio of the forward shock radius to the contact discontinuity) at 1000 years with different γ_eff values.