Temporal evolution of the semi-major axis a_p of migrating TOI- 216b. Horizontal axis measures the migration time t_mig (we do not show the simulation stages during which the planet was non-migrating). Solid lines are for α_DZ = 10⁻³ and dashed lines are for α_DZ = 5 × 10⁻⁴. Different values of α_MRI are distinguished by colour and specified in the plot legend. The shaded area marks the disk region over which α_DZ increases to α_MRI. Outwards from the shaded area, there is the dead zone. The MRI-active zone is located inwards from the shaded area.