How to increase texture cube resolution - (cubeMap - imported HDR image)

I’m importing a HDR texture and it is converted to texture cube (cubeMap), just as it should. But once imported, the resolution is 512x512x6, even if I set the mip gen settings to NO MIPMAPS. Is there any way that I can make the texture be displayed at native resolution, or at least 4k or 8k.

Also I’ve changed the reflection capture resolution to 1024 in the project settings.

I want to use the cubemap in a sphere reflection capture, and there are a lot of fine details.
Here is a screenshot of what the setup looks like (note that I’ve plugged in 4k hdr, but I also have others that are 10000x5000 pixels)