Contextual filters at a Views level

I have a View display set up to feed the 'browse existing' part of a browser. My browser is set up to show in a modal. I have a contextual filter on the view that looks at the URL and should filter by only Docs which have a certain field populated. It works in the Views preview, but doesn't come through to the modal - I see no results.

Is this supposed to work? I'd love to know that as a starting point so I can troubleshoot more effectively.

Thanks.