Hi,
without child theme on two different WP sites (both with Iconic pro Theme), I see the same result. For post pages and index (post list) page is the full width page template is unuseable. Has no effect.
I tested one other WP site with no themonic theme, there is full width template for pages avaiable too.. On this site i has the same result: post pages and post index page still be two-columns-page. Page template has no effect on post pages.
I read about this on WP support sites, so I think it is unpossible, that page-template has any effect on post page on your system (“Full width template is working fine at my end”). (?)
I resolved this problem manual, via editing in your single.php and index.php.
line 12.: <div id=”primary” class=”site-content” style=”width:96%; padding-right:3px;”>
line 74.: <?php // get_sidebar(); ?>
Ervin M.