First connect a variable to your tessellation multiplier, the higher the number you set, the higher the polycount will be, which will give you the result you are looking for. However UE4 has a cap on the tessellation multiplier, therefor you cannot tessellate the mesh enough to get the resolution you are looking for. You can tessellate your plane in your 3d modelling application.
You can also consider parallax occlusion mapping, which will give you the result you are looking for:
However this look like a simple material, and I would recommend you would just model it instead of using a displacement.
If you decide to use displacement, I would recommend you plug a map into the displacement multiplier where you can specify a high number of tessellation near the holes, and none on flat surfaces,
Like I said it has a cap, even if you put 1000, it will stay limited to 8.
It takes a scalar parameter, but you can give it a one channel map, that gives it different multiplier value for each pixel. Anyway stick to the occlusion solution it will fit best this example, just don’t use it too much as it will impact your performance if you use it alot
Just export a more dense mesh from your modelling application. That box, tessellated by a factor of 15( which is maximum, even if you put a thousand there), would not have enough geometry to displace individual tiles.