Hi,
I want to downsize the HDR in the dome light. But can't see any changes.
What is wrong about my settings?

Thanks.

Take this with a grain of salt, as my wisdom is limited.

You won't see changes in specular reflection from that setting, but rather on the diffuse side.
It's there to filter out high frequency pings in the map that would result in noise.

You can try the following, to see a visible result. Take your sphere, kill the specular reflection from the shader, and use

as your map. The light there comes largely from a small sun disc. If you decrease the maximum size now to something ridiculous like "5" or so, the sampling will miss the sun and the scene turns blue.

That USD Sphere primitive is the single most embarrassing thing in Houdini right now