I believe you're having a TV issue with overscan, and not a vega GPU issue. Try setting your TV to 'screen fit' or 'just scan' or 'native'. It could also be under 'game' mode or the like.I'm not sure what to tell you, aside from the definite fact that the HDMI scaling slider section of the Radeon software UI does not appear. I have tried everything, including a full factory reset. I can only conclude that the APU's graphic functions are limited. I've contacted AMD support several times, and nobody seems to be able to confirm or deny that HDMI scaling should be possible with Radeon and this GPU.
Essentially the TV needs to be 1:1 or its not going to work.