SteamOS Underscanning on 1080p TV

I have been trying to get Steam OS setup properly. I have it installed fully updated, but it will not fill the whole 1080p screen. There is a 1-2 inch border around the screen. All I want to do is stream from my main rig to the tv. Its an old dell box with a low end AMD R5, but it works fine with Windows 10 Preview. I have installed the latest AMD drivers, and can adjust the scaling to fill the screen in catalyst as root in desktop mode, but when I go back to steam Big picture mode it reverts. When I reboot it reverts in desktop mode also. I have tried all the workarounds, edits, cli entries and such found at the steam forums. I'm not a linux master by any means, but I can usually follow instructions. As an aside the streaming performance is abysmal compared to streaming to my windows laptop or the previous windows install. Is this still just a fun AMD issue with Steam OS? I know they were nvidia-centric when the software launched.

Any suggestions would be appreciated. Should I just install an Ubuntu based distro and add steam to it?

Have you checked the settings on the TV? I had a similar issue with a windows rig (the picture was too big for the screen even though my rig was outputting 1080p) and it turned out that the tv was doing wierd and wonderful things with the picture.

The TV says its 1080p signal coming in hdmi. I just restarted it again, and the grub menu fills the screen. Once it loads steam, it reduces the screen size about 7%. If i switch over to desktop mode and run catalyst as root I can move the underscanning slider up to 0. Which fixes the issue until i go back to steam or reboot.

Well I gave up on Steam OS. I just finished installing Zorin 9. Installed steam and all is well. iI hate being a lazy Linux newb, but iit just works now. No graphics , scaling, or streaming issues. I guess that''s why steam is still a beta release.

It's an AMD driver issue. Not sure if updating drivers will fix it yet but I'm sure they're working on it.