Registry settings will not help you to get this option in RadeonSettings. This option is controlled same way as Wattman. It checks your Device IDs. I already installed my Fiji as polaris10 and got all its registry. One more possibility to get it via registry is blind enablement: Someone with Polaris has to do 2 snapshots of registry. One with VSync OFF and another with EnhancedSync ON. Then we will try to use all vales which this changed. Killing RadeonSettings.exe and starting it again as it reloads Registry values and unless you go to particular menu, it will not change those registry.