Lens system configurations of the 2L1S (upper panel) and 3L1S (lower panel) models. In each panel, the inset shows the broad region including the positions of the lens components: blue dots marked by (M₁, M₂) for the 2L1S model and (M₁, M₂, M₃) for the 3L1S model. The dotted circle in each inset represents the Einstein ring. The source motion is represented by a line with an arrow. The red closed figures represent the caustics.