Is 16:9 supposed to fill the whole screen?
No as it all depends on what is being transmited, as there are a number of formats. So even in 16:9 you may still get black bars at the top and bottom of the picture, as the broadcsater is trying to show you more of the image.
If I set the digi box & the tv to 16:9 then BBC 1 HD has black bands either side of a tall picture & ITV 1 HD is full screen
Very strange.Something is autoformattinging the picture and stretching it, maybe some form of automatic "black bar" removal?