Inline entity form complex and cardinatlity

I am adding an ief type field to my form with the following

    $form['inline_entity_form'] = [
        '#type' => 'inline_entity_form',
        '#op' => 'add',
        '#entity_type' => 'my_ent_type',
        '#bundle' => 'my_bundle',
    ];

I am sure this is something under my nose that i am missing but how do i force this to complex and set a cardinality for this instance?

Grateful for any pointers
Mathew