You need a ‘contact shadow’ under those rocks. Ie a tighter shadow often produced by Ambient Occlusion.
Maybe another thing would be a little blending ‘fillet’ with a textured grad going along some of the bottom edges, to simulate thin layers of sand and dust that has blown up and collected along the base?
Not sure if you are going for photo real (probably not right?) but If so and that is meant to be a bright lit scene and you were ‘exposing’ for the bright parts then the shadows would be darker.
Maybe take a look at Journey see how they blend? Also take a look at real world photos and see how reality blends.