Is it possible to have sitemap with default permalink structure?

Hi,
I know it’s better to have other than default permalink structure, but in a specific site it should be like that. I use your great plugin in other sites but in this site with default permalink structure I can’t find a working sitemap.
In the plugin’s setting page it points to mydomain.com/sitemap.xml as the sitemap, but this url leads to 404 page.
I tried to go domain.com/?xml_sitemap=1
There I see a sitemap index generated by your plugin but then for example one of the links leads to domain.com/index.php?xml_sitemap=params=post-sitemap
and inside it there is the url of homepage and only one url that leads to
domain.com/index.php?xml_sitemap=params=main;html=true
and clicking it gets me to the same page.
Meaning – there are no posts in the sitemap index.
The same with pages.

Is it possible to use default permalink structure and a working well sitemap with your plugin?

Thanks in advance!