Wave for Polar graphs

Am I right in thinking that the waves called up by the Polar Graph pop-up can only be in the root: data folder?  

No, they can be in any data folder.

But the New Polar Graph panel shows only waves in the *current* data folder, whatever that might be.

Or drag the red arrow in DataBrowser to point on the folder you want to use.

Alternatively, left click the red arrow area while holding Option (Mac) key (ctrl or alt on Windows?).  

You can also right-click any folder and then choose Set Current Data Folder. And yes, it works with holding alt in Windows.