That’s not a good idea.
i have added adsense after paragrph 2 & 5 by editing /wp-content/plugins/accelerated-mobile-pages/templates/design-manager/design-1/elements/content.php
but after i updated amp for wp plugin all the adsense code vanished we need to use the plugin.
placing by short code involves lot of manual work for every page.
now i am trying to add a custom plugin for middle amp ads