adsense and posts page

hi everyone!
could anyone help me with this problem.
so you have front page and posts page. I’m think the posts page is pretty special because I’ve tried to put a google ad in the header for both single.php and page.php, but in neither does the ad show up on this particular ‘posts page’. The ad works in all other pages and posts. What can i do?

Sorry if this is confusing, but help would be much appreciated!
kind regards