ASync Reprojection not working on RX 480.

Have an RX 480 and Windows 10, and installed the latest Crimson driver that supports ASync Reprojection for HTC Vive however SteamVR is saying it's off, even when the option is enabled in SteamVR settings.

 

I have noticed others with this issue, hopefully someone can shed some light on this, is there a setting inside Radeon settings that I have to enable? I went looking but didn't find anything relevant.