I will try to add a column to the Document Grid which will tell you this number.
Can you send me one of your Skyline documents with some proteins and peptides in it? With new features like this, it's always good for us to be able to see some real world data where the feature is going to be used, so we can make sure that the feature looks right.
In Skyline you can use the menu item:
File > Share
to create a .zip file containing the Skyline document and supporting files including extracted chromatograms.
If that .zip file is less than 50MB you can attach it to this support request. Otherwise, you can upload it here:
By the way, do you know what we're supposed to do if the protein sequence has repeats in it, so that a particular peptide sequence can be found in more than one location in the protein sequence? My guess would be the peptide would get counted twice so that the % coverage is telling you the number of amino acids in the protein sequence which could belong to a peptide in the document. But, I could also imagine that the community might already have chosen a different convention as to what to do in this case.