Post Grid Thumbnail Size

Is there a way to change the thumbnail size loaded in the recent posts grid? I did a temporary fix in the code like below, is there a way I can make this change permanent? Or perhaps a selection could be added in the block, thanks.

if( $attributes[‘imageCrop’] === ‘landscape’ ) {
$post_thumb_size = ‘medium’;
} else {
$post_thumb_size = ‘ab-block-post-grid-square’;
}