Cannot get 100% mirror-like reflection from HDRP Lit shader

I'm playing with the HDRP Lit shader, but I find that I cannot get a perfect clear reflection image on a totally smooth plane. Even though I set the smoothness to 1, metallic to 1, the reflected image is not that clear(I thought it can be as clear as background).

Screenshot is below:


I set up a simple project with only an hdri sky and a little plank. Make the smoothness and metallic to 1. The reflected image on the surface is quite similar to a oil painting(full of tiny color chunks and the lines are jagged) while I thought it would be as clear as a mirror. You could focus on the fence edges, floor brick edges and the leaves in the screenshot above.

Is there any other settings I should tweak? Or it's normal that I cannot get a perfect mirror-like reflection on a totally smooth surface.

What I have considered:

1. Compression. I set compression of the hdri file to "none"
2. Post-processing. I only add four overrides: "Visual Environment", "HDRI Sky", "Fog", "Tonemapping". Adding "Fog" is to make sure that fog is disabled. So there is no post-processing blurring my final frame.

Thanks for any suggestions and discussion.

 

Seems you set lower resolution of sky reflection in HDRP asset.
Try to use higher resolution and see it works?

 

Thanks for your reply! I tried this setting, but it seems that "Reflection Size" cannot solve this problem.