I think it could be useful to collect here some, partly hidden commands related to raytracing of Foliage.
Please comment other usefull stuff for this topic
r.RayTracing.Geometry.InstancedStaticMeshes.Culling 0 → makes foliage visible in raytracing
r.Shadow.DistanceScale → higher values means higher distance of raytraded shadows
set evaluate world position offset in details panel → raytracing for moving parts like leaves