Comparison of the aspect ratio as a function of orbital distance for discs with mm grains with settling, without settling and with the settling of μm grains. The disc structure is almost the same when no settling is implemented and when the opacities correspond to mm grains, but the grains are distributed as micrometer-sized dust (Eqs. (17)–(21)). When settling is included the millimeter grains are concentrated near the midplane, leaving the upper layers with diminished opacities and enhanced cooling rate. Without efficient settling, the inner discs get hotter. However, this creates a shadow that prevents theefficient heating of the outermost regions from stellar irradiation.