If I use the folowing snippet then the text adds correctly with almost no spacing underneath...
$para_nogap = array(
'spacingBottom' => 1,
'font' => 'Futura Std Medium',
'sz' => 14,
'color' => '6c6241',
'caps' => 'on',
'rawWordML' => false,
);
$docx->addText('Header Text', $para_nogap);
However if I do the same but use 'rawWordML' => true and store in a variable which I then add to the document - I seem to lose the 'spacingBottom' and it resets to 200.