function _setBtnThreadHerePosition(welButton){
            var welThread = welButton.closest(".comment-thread-wrap");
            var nPadding = 10;

            // set unfold button right
            welButton.css("right", ((welThread.index() * welButton.width()) + nPadding) + "px");

            // set unfold button top
            // find target line with thread
            var welEndLine = _getTargetLineByThread(welThread);
            if(welEndLine.length > 0){
                welButton.css("top", welEndLine.position().top - nPadding + "px");
            }
        }
Set position of .btn-thread-here , which marks folded thread

@param welButton
@private