I changed the article_poster / article_hero fields to ‘group’ instead of ‘clone’ – and made a subfield called ‘image’ and then cloned that.
$poster = get_field('article_poster');
$posterSmall = $poster["small_crop"]["url"];
$posterMedium = $poster["medium_crop"]["url"];
$posterLarge = $poster["large_crop"]["url"];
but my first instant was to access [“image”] – which I didn’t need to do – because the clone just replaces that.