Displacement in distance faked by normal mapish trick?

[Ihno]

I read a few times here that Vray uses some kind of normal map trick to fake displacement details which are smaller than the edge length. Is that true?
I'm not really seeing this happening when I test. Also, I found no information about this in the docs.
When will this kick in? Only if view dependent 3d displacement is used? I would really love to have this feature and maybe a parameter to tweak the strength or at least a checkbox to activate/deactivate it.
Or at least some more information about this.

I'm currently wondering if I should generate a displacement map in Zbrush form the lowest subdivision level. And then generate a normal map form a higher subdivision level. To cover the really small details which the displacement can't cover due to a 4px edge length.

But then I have dynamically changing geometry below the normal map and I believe that probably isn't working well... Maybe I should use a bump map instead...
Anyway, I want to know more about what vray does with the displacement alone.

[Ihno]

I take it back. I can clearly see it happen now with 3d displacement. Dont know what I did wrong before.