Adaptive Sizing is an option that can be seen when editing or adding a placeholder to your site:
Adaptive Sizing is an intelligent system that analyzes when to show multiple smaller ad sizes in a larger placeholder. An equal or lesser amount of pixels are shown, but there are multiple ad creatives rather than one, larger one.
For example, as you can see on the site below, there is one single in-content ad showing:
However, there are two creatives showing in this specific sized placeholder:
Depending on the placeholder, there can also be more creatives than just two. This behavior is normal, and is a result of our incredibly clever machine-learning system having been able to determine that showing more creatives is delivering the highest returns in terms of your EPMV - or, in other words, the best possible balance between revenue and user experience!