Orientation, ∆ϕ, of the isophote ellipses relative to the orientation of the innermost ellipse drawn over semimajor axis a. A negative value of ∆ϕ means clockwise rotation and a positive value counterclockwise rotation. Solid lines are used for the systems with inner perturbers and dashed lines for those with outer perturbers, and rows are used to show four different wavelengths tracing small halo grains: 2 µm, 10 µm, 21 µm, and 70 µm.