Super simple if you know how I guess - how do I modify the below code in the 5.7 standard Page List block to pick a specific thumbnail (say 'small' for example)?

<?php if (is_object($thumbnail)): ?>
<div class="ccm-block-page-list-page-entry-thumbnail">
<?php
$img = Core::make('html/image', array($thumbnail));
$tag = $img->getTag();
$tag->addClass('img-responsive');
print $tag;
?>
</div>
<?php endif; ?>

(Wrapping this in my own mark-up and CSS but based on the standard page list block.)

Thanks for any help anyone might have!