prompt-for-directory scroll-window size

The current (LW5.1) version of prompt-for-directory shows a scrolling
option-pane with height of 6 visible choices.  I would like to have it
appear with more, say 20; I have tried many permutations of :pane-args
and :popup-args, and with them :height, :visible-min-height, etc. without
affecting it.  Is the size truly not specifiable, or did I give up on the
init args before finding the magic combination?
                                                                                
  Raymond Laning                                                                
  Principal Systems Engr                                                        
  Missile Systems                                                               
  Raytheon Company                                                              
                                                                                
                                                                                
                                                                                
                                                                                
  520.794.7924                                                                  
  rclaning@raytheon.com                                                         
                                                                                
                                                                                
                                                                                
  1151 E Hermans Rd                                                             
  Tucson, AZ 85756    www.raytheon.com                                          
                                                                                
                                                                                
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