@Levin Meienberg Run with the best-selling products, but include all sizes. I haven’t found a lot of success with PMax, or at least it’s an uphill battle to reach your goal with so few products in one campaign. I don't have the exact explanation, but it’s something I've observed when running PMax campaigns with fewer than 15 products compared to 100+. Another "black box" trick I’ve discovered is that when you add these best-selling products to your PMax campaign, don’t add them by each product ID. Instead, use a custom label for the best-selling products and select that entire custom label as a listing group. Again, I’m not sure why, but having too much segmentation within a PMax campaign has resulted in worse performance. I almost always see a jump in performance when I stop selecting products individually and use groupings (i.e., product type, brand, custom label). Hope that helps!