First filed here: https://bugzilla.redhat.com/show_bug.cgi?id=277911

several zenity modes don't respect --width and --height.  The problem is pretty
simple, in /usr/share/zenity/zenity.glade, the widgets/windows for the modes
have resizable=False, when it should be True, such that the C-code changing the
size actually has an effect.  For example-

<widget class="GtkDialog" id="zenity_question_dialog">
  <property name="border_width">5</property>
  <property name="title" translatable="yes">Question</property>
  <property name="type">GTK_WINDOW_TOPLEVEL</property>
  <property name="window_position">GTK_WIN_POS_CENTER</property>
  <property name="modal">False</property>
  <property name="resizable">False</property>
                             ^^^^^

If you change that to True, then "zenity --question --width=640 --height=480"
will work as it should.  There a few others with the same bug, just search for
resizable in the .glade file.