Hi guys,I am having some problem using the displacement,so I have think to ask for help here (& probably based on most of you knowledge this should be a noob problem/question,so forgive me for that) 
I am modeling a rock that need to go in game,& as suggested from a friend I am following this workflow: Sculpt in Zbrush,decimation of the sculpt for have the low poly,unwrap of both & following the tutorial on youtube “Baking matcaps to texture maps”,then all into topogun to bake this matcaps from the high poly to the low poly
Now,the problem is this,as you can see in the image below on top there are 2 images of the hp sculpt with the matcap skeleton,the two images on the bottom are the same rock but with the texture on it,grabber following the tutorial on youtube (matcap on a plane with displacement) & there you can see really nasty things,like if the generation of the displacement map was wrong in some way.
I have no clue about what is happened,the reason I was thinking about was because for have a better topology in the hp sculpt I have done a better mesh in max,imported in zbrush & converted into the actual sculpt by using Divide+Project all,& this mesh come from max with some smoothing groups,so I was thinking that maybe the SG’s was interfering with the diplacement creation…
Really no idea,so actually I am stuck,I really appreciate if someone can explain me what is happening & why I am failing on generate a proper displacement map,here another image, the flat plane with the displacement on it (intensity 1,as you can see the unwrap is divide into 2 uv shell,one for the rock & one for it’s base(with a lower density),I do that to have less distorsion on the rock),help me please 
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