I'm using the Tabular Message View with Extras. It looks great when I use a link into the middle of the discussion.

However, when people come from the top level downinto the discussion, the view is not tabular.

How can I make the view tabular?

You have chosen to have "Threaded View" as the default when entering a discussion so you are seeing the threaded overview first.

Deselect that option in either the Control Panel/Discussions (for the entire site) or by modifying the options at the folder level by EDITing the folder and choosing the Threaded Message Settings.