Continuous resonance index κ for a pair of 10⁻⁵ M_⊙ equal-mass planets as a function of the rescaled surface density Σ_0,gap (Eq. (22)) and the disk aspect ratio h₀. The green line verifies Σ₀ ∝ h², corresponding to a constant migration timescale. The yellow line is an example of the fitted . The dashed black line indicates the gap-opening threshold, h₀ = 0.02. See Fig. 1 for a complete description.