Yes, the fullscreen version shows more in this case. In most open matte cases, though, the widescreen is still the better way to go, because it was shot that way simply to be easier to carry over to home video (before consumers cared about widescreen), and the directors usually didn't pay attention to the edges of the frame resulting in things like boom mics and other mistakes being in the frame. In this case, Zemeckis has sometimes stated things to the extent that he intended the movie not to be wide, so it's debatable. There aren't any mistakes in the full frame. But, yeah, that explains the whole misframing fiasco in the first place because they were covering up the edges of the picture in wrong places omitting important information.