Usage of EditorAreaCSS and ToolbarComboPreviewCSS

This question may be rooted in a misunderstanding of what FCKeditor can do... please tell me if so.

I am attempting to reference a custom css file so users editing content can select the style from the "style" dropdown box in the toolbar. I *thought* the docs indicated that I can just change the EditorAreaCSS to include the path to the CSS file (for altering the editor itself) and the ToolbarComboPreviewCSS so my defined classes in my CSS file will be options in the "Style" dropdown.

I need to reference a dynamically named CSS file, so in my HTML code that calls the editor, I define fckEditor.ToolbarComboPreviewCSS = '/mystyle.css'; I cleared my cache and nothing seems to change. The Style dropdown still just has the standard "Custom bold" "Custom italic", etc. I know there is a fckstyles.xml file, but I thought the point was the ability to just point to a CSS file and use those defined classes. Is this how it is supposed to work?

What am I missing? Any help is appreciated.

Tim