ComboBox height?

CB_SETITEMHEIGHT sets the height of the combobox window, but has no effect on the dropdown list.

CB_SETMINVISIBLE seems to be the right message, but it always fails when I try it:

Const CB_SETMINVISIBLE=$1701

window=CreateWindow( "ComboBox demo",0,0,160,120+80 )
combobox=CreateComboBox( ClientWidth(window)/2-64,ClientHeight(window)/2-12,128,500,window )

For k=0 To 50
	AddGadgetItem combobox,"Item "+k
	Next
SelectGadgetItem combobox,0

hwnd=QueryObject(combobox,1)
result=SendMessage(hwnd,CB_SETMINVISIBLE,40,0)
If Not result Notify "SendMessage() failed."

While WaitEvent()<>$803
	If EventID()=$401
		If EventSource()=combobox
			Notify "Item selected:"+SelectedGadgetItem(combobox)
		EndIf
	EndIf
Wend

End

See the MS docs:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/shellcc/platform/commctls/comboboxes/comboboxes.asp