There is the so called "Index" attribute that is available for indicating a file's place, among the entire set, which is visible in the file window. Is this "Index" available while working with XAML code of the IMatch File Window Tip?
This attribute exists only within the File Window and you can use it to show the index in your layout.
The file window generates this index dynamically, while laying out the files in the scope.
There is no corresponding variable you could use to show this index in the File Window Tip.