Hello,
Seems I can't get proper displacement with RPR.
This what I'm trying to achieve . This done in V-ray for Maya

and this what I got in RPR

with maximum subdivisions what RPR settings letting me set "8"
the only way to get better result is to heavily subdivide geometry.

still not perfect but something, render time also increased dramatically.
Increasing displacement subdivisions not make any difference but only increasing render time.