I am not from Intel, but you may find that most BIOS since the original may require that the HDMI TV support 1024x768 resolution (at 60Hz?). On my displays this comes up as small display in center. I am not sure but some TVs may have a particular HDMI input (such as 1) which they suggest for computers because it supports such varying resolution.
It seems crazy to me - Intel motherboards before the NUC (including integrated video from the processor chip) display okay full sized on all my monitors/TVs. Early NUC may have also. But then Intel revised the BIOS and now all NUC seem to display that tiny screen in center.