Final value of the continuous resonance index κ as a function of the rescaled surface density ∑_0,gap and m_p for systems with m_p = m₁m₂/2. The inner planet is fixed at the inner disk edge, and the initial conditions are otherwise the same as in Fig. 2. The dashed black line is the gap-opening threshold. Except for a few systems, planets with masses below 10⁻⁴M_⊙ that would otherwise be captured in 2:1 do not stay there due to overstability.