Simulated magnification across the arc in the lens plane. The critical curve is at the origin. A perturber with 10⁴ M_⊙ is placed ≈007 from the critical curve. Colors show three assumptions perturber profiles: light blue for a point source, dark blue for a Gaussian profile with σ = 10 pc and red for a Gaussian profile with σ = 20 pc. Left panel shows a wide range, and the right panel is a magnified version around the perturber.