Box import with FPDI

Question

I import a template with php and fpdi to add some stuff and to save it as a new pdf on my server.

The code looks like that:

$pdf = new FPDI();
    $pageCount = $pdf->setSourceFile(Config::PDF_TEMPLATE_FOLDER . $template);
    $pdf->setPageUnit('pt');
    $pdf->SetPrintHeader(false);
    $pdf->SetPrintFooter(false);
    $pdf->setJPEGQuality(100);

    foreach ($contentData->pages as $page) {
        $tplIdx = $pdf->importPage($page->index, '/MediaBox');
        $size = $pdf->getTemplateSize($tplIdx, 0, 0);
        $orientation = 'portrait';
        if ($size['w'] > $size['h']) {
            $orientation = 'landscape';
        }
        $pdf->setPageOrientation($orientation);

        $pdf->addPage($orientation, array($size['w'], $size['h']));
        $pdf->useTemplate($tplIdx, 0, 0, $size['w'], $size['h'], TRUE);

    }

When i look at Acrobat Pro i can see the Page Boxes of my template are different to the page boxes of the generated pdf.

Here from my template:

And here from the generated PDF:

How can i add the Margins to the generated pdf?

Thanks,

Marc