A maioria das TVs tem overscan ativado por padrão; veja se você pode desativá-lo no menu onboard da TV.
Overscan is a behavior in certain television sets, in which part of the input picture is shown outside of the visible bounds of the screen. It exists because cathode-ray tube (CRT) television sets from the 1930s through to the early 2000s were highly variable in how the video image was positioned within the borders of the screen.
Source: Wikipedia
Se o overscan estiver ativado, isso acontecerá, o que é exatamente o que você descreveu: