Вы можете добавить что-то вроде этого:
$tagvs = array('h1' => array(0 => array('h' => 1, 'n' => 3), 1 => array('h' => 1, 'n' => 2)),
'h2' => array(0 => array('h' => 1, 'n' => 2), 1 => array('h' => 1, 'n' => 1)));
$pdf->setHtmlVSpace($tagvs);
А вот описание формата из документации / примеров:
Файл: tcppdf.php:
/**
* Set the vertical spaces for HTML tags.
* The array must have the following structure (example):
* $tagvs = array('h1' => array(0 => array('h' => '', 'n' => 2), 1 => array('h' => 1.3, 'n' => 1)));
* The first array level contains the tag names,
* the second level contains 0 for opening tags or 1 for closing tags,
* the third level contains the vertical space unit (h) and the number spaces to add (n).
* If the h parameter is not specified, default values are used.
* @param $tagvs (array) array of tags and relative vertical spaces.
* @public
* @since 4.2.001 (2008-10-30)
*/
Файл http://www.tcpdf.org/examples/example_061.phps:
// REMOVE TAG TOP AND BOTTOM MARGINS
//
// $tagvs = array('p' => array(0 => array('h' => 0, 'n' => 0), 1 => array('h' => 0, 'n' => 0)));
// $pdf->setHtmlVSpace($tagvs);
//
// Since the CSS margin command is not yet implemented on TCPDF, you
// need to set the spacing of block tags using the above method.