Morphing set of gravel stones over surface

Hi

I have the following problem. My intention is to distribute and adapt a set of gravel that act as a unit on a given surface. I tried with the definitions of
"Morph", first dividing the domain of the surface, proving Isotrim, etc, but always generated a grid that does not follow the alignments of the surface and is within the boundary. I think the solution is not very complex but I can not see it.
Does anyone could help me out?
Thanks in advance.
I leave the files below.
Greetings