It doesn't matter. Just put it down regardless. This is part of the scientific record. People will know that a poster is usually less effort than a paper, and that a 2nd, 3rd, etc. authorship is less than a 1st authorship. It may not mean much, but it is not resume padding to include very peer-reviewed paper and (inter)national conference-presented poster, regardless of where you are in the authorship, in your application.