Bulk setting Symfony form field values with setData in SF4.4

In my Symfony 4.4 application I have the following code inside my controller. I am attempting to pre-populate the form based on previous submissions or data pulled from the database. Importantly, the DetailsType form includes multiple entities so it's not a clean 1 entity per form setup here.

    $postVars = $request->request->all();

    $formData = [];
    if (count($postVars) > 0) {
        $formData = $postVars['crmbundle_register_details'];
    }

    $form = $this->createForm(DetailsType::class, $formData, [
        'attr' => ['class' => 'reCaptchaForm'],
    ]);

    $form->setData([
        'firstname' => $person->getFirstname(),
        'lastname' => $person->getLastname(),
        'email' => $person->getEmail(),
        'country' => $person->getCountry(),
        'timezone' => $person->getTimezone()
    ]);

My problem is if I try to pre-populate the form with setData above it does not work.

If I do it individually as below it works, but I can't see why. I'd prefer to pass setData an array rather than call setData multiple times.

$form->get('firstname')->setData($user->getFirstname());
$form->get('lastname')->setData($user->getLastname());
$form->get('email')->setData($user->getEmail());
$form->get('country')->setData($user->getCountry());
$form->get('timezone')->setData($user->getTimezone());

If the form contains many entities, it's better to have an embed form for each entity. In this case, you don't need to call the setters at all. The controller action code will be:

$form = $this->createForm(DetailsType::class, $someParentEntity, [
    'attr' => ['class' => 'reCaptchaForm'],
]);
$form->handleRequest($request);