Toolbar button dropdown width

I have a toolbar button with a panel as the dropdown control. The panel has a width of 200. The dropdown control shows a width of 200. Dropdown width for the button = 200.
When the dropdown is displayed, it is the same width as the button.
Is there something else I need to set to ensure the dropdown has the extra width ?

TIA,
Sue

It's OK. I've just found the DropDownAutoWidth property. Setting to false solves the issue.