View -> Tool Bar, Status Bar, Page Slider, or Scroll Bar can erase the tool bar, status bar, page slider, or scroll bar.
Therefore, preview view portion becomes somewhat wide for the dviout window.
One may use Presentation Mode to display with no frame.
One may also use Presentation Menu->Cut edge.
Specifying the parameter -NULL: in the command line, the whole display of CRT is used for Preview (cf. Start and Exit).