I found that I get full screen when I select a channel to watch live from the guide, but not when I add a channel to Favorites, then select it to watch from Favorites.
I don't see that there are SD and HD versions of channels in the app guide, as some people suggested here and in similar threads. They all seem to be HD - the picture is crisp HD either way I select the channel, and the channel number is the same in Favorites as it is in the guide. So it's not an HD vs. SD issue. It seems to be where you launch the channel from, which is a bug in the app.
