How to add a $form to a group tab?

Hi i'm trying to insert a form coming from a module into the node_form but i can't figure out what the id of a particular group is to call it in the $form code.

Here is my code (from the plugin):

  $form['products'] = array(
    '#type' => 'fieldset',
    '#title' => t('Products'),
    '#group' => 'additional_settings',
    '#collapsible' => TRUE,
    '#collapsed' => TRUE,
    '#weight' => 5,
    '#tree' => FALSE,
    '#attributes' => array('class' => array('container-inline')),
    '#prefix' => '<div id="participants">',
    '#suffix' => '</div>',
  );

This code works but it inserts my form in the additional_setting area (vertical tab) of the node_form but i want it to be inside a particular group (the id of the horizontal tab group is "group_order" and the horizontal tab is "group_order_1").

Is this possible?

Thank you!