Same as lower panel of Fig. 2, but here we plot the GT criterion as the azimuthal average over positive grid cell values around the spot. Cells with negative (stable) values are not considered. The horizontal green line represents the azimuthal average of the τ = 1 surface. The vertical green lines mark the average position of the umbral and spot boundaries. In magenta we draw flux surfaces, that contain 7, 28, 51, 62, 68, and 74% of the total flux respectively.