I was referring to the fabric eelpout and RLead8 were talking about. When I got my Gravity it had a strip of flocking inside the HUD frame that I hadn't seen before and apparently that only some people that have recently taken delivery have. While it doesn't do anything for the reflection of the HUD's frame I wonder if it was placed there to mitigate the "blue blob" reflections many earlier deliveries suffered from, I can't see any other use honestly.
I also think that there's a case to be made for removing the plastic shroud and coating it in a more non-reflective material. If it's at all easy to remove the frame I'd probably want to go with the same kind of flocking that a lot of people use to remove reflections on the dashboards of race cars. I'd probably also consider it for the air vent to the right of the HUD as that also has a reflection in the windshield a lot of the time too.
I've seen cars with dashboards done in this material and it definitely works, it's just a bit of a pain to do:
https://www.flockit.com/