Thank you for responding to my inquiry and clarifying where it looks for the mobile "mask". My site has user friendly URLs in which mobile pages have "Mobile-Page" as part of the file name, not a unique subdomain or parameters. It would be nice if the file name was also checked for the mask, perhaps with a choice of what part of the URL to look for the mask. Anyway, I modified the program so it adds the parameter "mgui=y" to mobile page URLs and set "mgui" as the mask and it correctly creates a mobile sitemap as desired. This runs counter to the concept of having user friendly pages though.
Since there isn't a way to separate mobile pages from desktop pages in the HTML version of the sitemap, I changed the program so it adds "(Mobile Page)" or "(Desktop Page)" to the end of the page title since that is what is displayed in the list. Hopefully visitors that are looking at sitemaps are smart enough to determine which type they want to view. It still would be nice to have separate HTML versions of the sitemaps so the relevant one could be shown.