The best way to set any given program so that it comes up in a window of the desired size is to do a little dance involving the Restore command in the Window commands, which are reached by clicking in the absolute top right of the window.
Here's the drill. Open that two-thirds display and use the mouse to make it the size you want it to be when it comes up.
Next, go to the upper right-hand corner and click in the big square box (the Maximize command). Now go to the upper left side of the window and click on the Restore command in the resulting drop-down menu.
The window will go to the size you set it for. Now close the window by clicking the X in the upper right-hand screen.
(Courtesy of Jim Coates)