Stange behavior with upscale

Hi everyone,
I was playing around with thumbs (ver. 2.4.1) to try and resize (increase or decrease) an image in a structure by width. I was not having much success and read on the forum that width would only work on images for reducing image size.

The following snippet shows what I was attempting with images smaller than 400 in width. This did not work and the image size was not changed.

<div class="one-third-column">
<?php foreach($pagecontent->sideimage() as $sideimage): ?>
<?php $sidephoto = $page->image($sideimage)->thumb([
'quality' => 80,
'width' => 400,
'upscale' => true]); ?>
<img alt="" src="<?= $sidephoto->url() ?>">
<?php endif ?>
<?php endforeach ?>

The strange behavior occurs when โ€˜widthโ€™ is replaced with โ€˜heightโ€™. When this is done, the image will resize to the given height.

is there a reason this canโ€™t be done with โ€˜widthโ€™?