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,