So this site is live now, so perhaps some links will help. I disabled my redirect, so you can see both pages.
I have 2 pages and both are identical /posts and /blog with content
I currently have /posts/ set as my static blog page, and am redirecting to blog to get the format I desire with the above shortcode.
If a switch the static page to point to /blog, then the default format (from where?) is shown, and not the wpshowposts shortcode version.
The above coding works on the category and CPT archives, just not the main archive.