Visual Basic - ComboBox

Hola:
Necesito agrandar la seccion donde el combo muestra los items(Coleccion de Items) sin agrandar la cabecera del mismo.

Option Explicit

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Long) As Long
Private Const CB_SETDROPPEDWIDTH = &H160
Private Sub Form_Load()
' Set the width for the dropdown list.
SendMessage Combo1.hwnd, _
CB_SETDROPPEDWIDTH, 310, 0

' Select the first choice.
Combo1.ListIndex = 0
End Sub