How to improve UMG UI text clarity in VR

I have written an UI system using UMG and put it into game world using 3D widget. The overall quality is very blurry. I tried to use stereo layer instead and the quality is much better. However, it is rendered on top of everything, but I need to render virtual hands to interact with 3D widget. I learned Oculus VR supports depth buffer, but I am using OpenVR/Steam VR, so depth support does not work. Is there any work around?

I also found out if I import UI as png and put it into game world as the texture of a plane, the UI seems clearer than UMG because texture supports mip. But I have to use UMG for more complicated interactions. Is there a way to enable UMG to become clear in VR?