I recall in UDK that I could set the desired pixels per meter texture density, and then there was a render mode that displayed each asset's density in shades blue-green-red. Is there something similar in UE4?
Are the UV coordinates snapped to the pixels of the resolution of your map? Maybe one of the islands is flipped? Also is there a reason you're using a normal map for the box?
Considering that Crysis does it per vertex, and you do it per pixel (I assume), wouldn't that make it terribly slow in comparison to the Crysis solution?