AMP with html extension does not work

Hi, my posts have an html extension. I achieve this by selecting a customized structure in the permalinks by setting /blog/%postname%.html

However, when I activate your plugin, it works for the homepage showing at http://www.mysite.com/amp an AMP modified homepage.

But when clicking on one of the blog articles, it goes to
http://www.mysite.com/blog/article1.html/amp , but does not show an AMP modified page, but the normal page.

I guess, it is because of my permalink setting with html extension? How can I mitigate this? Is there any possibility to add the amp in the beginning of the URL like
http://www.mysite.com/amp/article1.html?

Best regards

Adam