Path for a Views 3 page
I do not believe that a path such as %/% in views will work.  Have you tried it?  

The path factsheet/%/%  is not intercepting other content, it is the path to the view page.  That means that views responds to any page with a factsheets followed by other path segments.  The reason for defining the view pages with % is to create a wildcard variable to be used in contextual filters (3rd column of the main view form).  These filters supplement the basic  filters defined in the first column.  Having two % filters means that you can use two contextual filters.  The top contextual filter takes the first % and the second takes the next % in the path.

The Views preview works because you are only testing the contextual filters.  The path is not being run through Drupal to determine content.