Ratio of polarization cross-sections of imperfectly aligned dust grains C_x, to perfectly aligned dust grain C_p in the mid-plane of the model space for the C01 model (top row) and C02 model (bottom row). The x stands for IDG alignment (left column), RAT alignment (middle column), and GOLD alignment (right column). In the middle columns, dotted white lines indicate the regions where the alignment efficiency Q_Γ(ϵ) is at its minimum. The dotted red lines in the right column show the transition where GOLD alignment changes the sign of linear polarization. The areas A−D correspond to that of Fig. 5.