Description

This appears to be happening with portrait images with layout="responsive" for the pan-up and pan-down presets.

[Demo story](https://stories.nws.ai/amp/1288491817/test-pan-effect-adrian/#page=201c9eb1-9347-4ad2-92f7-f4833fb61984

)

Reproduction Steps

Create a amp-img with the animate-in="pan-down" layout="responsive" attributes in a template="fill" grid layer.
Be sure the image is a portrait aspect ratio image.

<amp-story-page id="pan-down">
  <amp-story-grid-layer template="fill">
    <amp-img animate-in-duration=".8s"  animate-in="pan-down" layout="responsive" src=<portrait image> width="1200" height="1601">
    </amp-img>
  </amp-story-grid-layer>
</amp-story-page>