code: function checkHeightCriteria() {
  
    var scrollY = scrollElement.hasOwnProperty('pageYOffset') ? scrollElement.pageYOffset : scrollElement.scrollTop;
    scrollY = scrollY + window.innerHeight * 0.9;
  
    boxes.forEach(function(box) {
        if( ! box.mayAutoShow() || box.triggerHeight <= 0 ) {
            return;
        }
  
        if( scrollY > box.triggerHeight ) {
            // don't bother if another box is currently open
            if( isAnyBoxVisible() ) {
                return;
            }
  
            // trigger box
            box.trigger();
        } 
      
        // if box may auto-hide and scrollY is less than triggerHeight (with small margin of error), hide box
        if( box.mayRehide() && scrollY < ( box.triggerHeight - 5 ) ) {
            box.hide();
        }
    });
  }
docs: check triggerHeight criteria for all boxes