Effect of the millilens profile. Comparison of millicaustics for four millilenses under the influence of the same macromodel magnification (|μ_1m| = 23) but for different mass, core size R_c, truncation radius R_max, and exponent α. The profile is defined as ρ(r)∝(R_c + r)^−α. The image shown in grayscale is the sum of the four magnifications from the four millilenses. The caustics for the two millilenses with mass 10⁴ M_⊙ and slope α = 2 are nearly identical and fall on top of each other, indicating that the mass is the main driver defining the size of the caustic region. The largest millicaustic corresponds to a millilens with four times more mass, and larger core and truncation radii, but the same slope α. The area above μ = 100 is a factor of four larger than in the smaller millilenses. A third millilens with the same mass, R_c, and R_max but a shallower profile (α = 1.5) behaves as the larger millilens with α = 2 but a mass of 2.93 × 10⁴ M_⊙, owing to the reduction in mass within the Einstein radius. Even shallower profiles (α ≲ 1) with large cores result in subcritical millilenses (no caustics or cusps). On the other hand, a steeper profile with α = 3 or greater produces a millicaustic almost indistinguishable from the one obtained when α = 2.