XF 1.3 Problem with displaying ads on my forum

Hello ,
I edited "ad_message_below" to show ads right under the thread message and its working fine , The problem is that it repeats under every post on the thread , I just want it to display just under the first post of the thread .
This fixed it ,
<xen:if is="{$post.position} == 0 AND !{$message.conversation_id}">
This content will show after the first post on the first page only

Thank you very much! .