XF 1.1 Sorting criteria in active member block

[kankan]

Hello,

I am looking for a way to customize the block "most active member" on the page member_list
so that it can display the most active user in the month.

I found this piece of code in the template but don't know how to change the code for that purpose :

   <div class="section activeMembers">
     <div class="secondaryContent avatarHeap">
       <h3>{xen:phrase highest_posting_members}</h3>
       
       <ol>
         <xen:foreach loop="$activeUsers" value="$user">
           <li><xen:avatar user="$user" size="s" text="{$user.username} ({xen:number $user.message_count})" class="Tooltip" title="{$user.username}, {xen:phrase messages}: {xen:number $user.message_count}" /></li>
         </xen:foreach>
       </ol>
     </div>
   </div>

Any help?

Thank you!