High poly mesh or Displacement


Hi Guys i am currently busy working on a project, and was wondering:
When you export a 16000Poly mesh from z brush to Maya create a displacement map for it, with 5 subdivide, why when i take it into Maya does it fatten instead of sharpen. My High poly version sub div 5 in z brush is around 4.1 mil poly.

And if this is an inevitable problem, is it worth raising the lowest sub div to a higher amount, use sub div 3 instead of sub div 1? fixing the scaling issue? because this is a full film, which means i will be needing a lot of poly space, and raising this number will mean a slower Maya, slower render and Doom.!