1. Check Preferences/Doent/Remember window size and location.
2. Open a new doent. Resize the window to preferred size by dragging the
lower right corner. Save the file as a Template file.
3. In Preferences/Doent/New Doent Template, select the new template
It should now give you a window of the desired size. I'm on FHMX, but I'm
pretty sure it has worked this way since at least FH9.