Light leaking with one sided geometry and dynamic shadows

Is there a trick to get rid of the light leaking with one sided meshes?

I can get it to cast shadows with “cast shadows as two sided”, or change the material to two sided, but the light artifacts are still present.

  1. The mesh seems to self-shadow as if it was in the light at certain angles.
  2. The light leaks at the bottom where the mesh intersects with the landscape.

A workaround is the make the mesh whole, but that takes a lot of time.