Hi,
1. The ‘at least one match..’ should work in this case. I suspect that you might not have the latest version of the plugin installed, as I recall there was a change in this logic in the recent 5 or 6 releases. Please make sure that the latest release is installed, version 4.11.5.
I’ve tried to replicate this behavior on my test environment, but I was not able to. I’ve made a category and post tag filter, and then choosen a category and all the tags – but only the posts that matched both at least one tag and the chosen category was displayed, correctly. I guess the update will solve this then.
Sidebar widget issue fix
A possible solution is to maybe use this plugin, which enables shortcodes as sidebar widgets. Then you could place the plugin shortcode there.