Thanks for your answer.
So, if I understand well your answer, this code should work isn't it?
$docx->replaceVariableByHTML('CHUNK_1', 'block', "<- Should not have a space before thhis text<br />End of the text", array('removeLineBreaks' => true));
Because it is not :o(
P.S. : I don't have access to the TIDY settings