After you located the configuration of the given search dialog, look at <IdList section of the <searchConditions section. Every <IdName line adds an object type to the "Type" list.

Add more object types if you want, remove some, or change the order.

<searchConditions>

 <SearchNode 

         xmlns="http://www.teradp.com/schemas/GN4/1/SearchConditions.xsd" 

         xsi:type="SearchConditionList" 

         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

   <List 

                 Op="In" 

                 Path="ObjectType.Id" >

            <IdList>

              <IdName Name="article" />

       <IdName Name="img" />

      </IdList>

    </List>

  </SearchNode>

</searchConditions>