Map of Ndiv(ℱ_tot) with an active fraction ξ = 0.6 and using the same conventions as in Fig. 4. The contours are spaced linearly between the minimum and the maximum of Ndiv(ℱ_tot). The maximum value for the positive blue contours corresponds to Ndiv(ℱ_tot) ≃ 4200, while the minimum value for the negative red contours corresponds to Ndiv(ℱ_tot) ≃ −3200. As expected, one recovers that when the active fraction of the disc is increased, the susceptibility of the disc is increased, so that the norm of Ndiv(ℱ_tot) gets larger and the secular diffusion is fastened.