UE5-Main now contains a new reflection denoiser, which makes reflections in this scene quite a bit sharper. Attaching A/B comparison screenshots.
One major missing piece is number of rays per pixel. In this scene your standalone reflections were set to 8 rays per pixel, but we don’t have this control in Lumen reflections at the moment and they trace only 1 ray per pixel. We’ll investigate adding a similar control to Lumen Reflections, but at the moment the only way to improve it is increasing general screen resolution with screen percentage.