Look for this line in qa-page-question.php:
$editor->get_field($qa_content, @$incontent, @$informat, 'content', 12, $formrequested),
And change 12 to whatever you like.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.