How to theme a paragraph form

Question

I would like to create a twig template for the form displayed inside the paragraph widget.

The only way I found is:

function mymodule_field_widget_paragraphs_form_alter(&$element, &$form_state, $context) {
// Check that the subform is opened  
if (count($element['subform']) > 2) {
    $element['subform']['#theme'][] = 'form__aw_calculator';
  }
...
}

After that, I have created a twig template form--aw-calculator.html.twig like the following

<form{{ attributes }}>
    <div class="grid--all three--columns">
        <div class="column column--first bg--red-level-3">
            {{ element.field_calc_ts }}
            {{ element.field_calc_ts_greenlight }}
            {{ element.field_calc_budget }}
            ....

Unfortunately, this is half working... some of the fields are displayed some other are not (the form mode used in the paragraph widget setting should display all of them) More over, I can't see the markup coming from my twig....

I have the feeling that this is not the right way to handle this... any idea ?