Normalised kernels associated with dust with respect to distance for different dust-to-gas scale heights, η. The dust-dust, K_dd, and dust-gas, K_dg, kernels are insensitive to η at large distances, an aspect also in agreement with the SL prescription (see Fig. 13 of Müller et al. 2012). The dust-dust kernel scales with 1/η at short range, which suggests that the SG acceleration due to dust can be comparable of the one of gas even for Z=Σ_d/Σ_g=0.01. At short distances, the normalised dust-gas kernel converges quickly towards $\sqrt{2}$ (i.e. with respect to decreasing η). As a consequence this kernel adopts a nature akin to the kernel associated with a planet-disc interaction.