Hi!
I've managed to put banner after every third post in main blog page.
I did it through ATO Style and edit center column and there I added
<?php if ( $bfa_ata['postcount'] == 3 ) { ?>
...banner code...
<?php } ?>
So, there it says that if I put something like <?php if ( is_front_page() AND $bfa_ata['postcount'] == 3 ) { ?> it will show only on FP.
And what would it be for single post page?
Thanks!