I think this depends on how your nginx is configured. Does it serve on both HTTP and on HTTPS (ports80/443)? Or does it a redirect from http:// to https://? (301)? I have no experience in "default server - option for HTTPS", but here is a discussion about it: http://serverfault.com/questions/578648/properly-setting-up-a-default-nginx-server-for-https
--good luck : )