Yes, it really matters if users can see the pop-under ad. If the ad opens behind the main browser window and the user never sees it, then there’s little chance of getting clicks or any real action. Some users may close their browser without even knowing a pop was there. This wastes your ad spend and gives no results. A good pop-under should load properly and show something that catches attention when the user finally switches tabs. Visibility is a big part of why some campaigns work better than others. How do others handle pop-unders to make sure they’re being seen by users?