With the Ezoic ad tester, you are encouraged to place between 15 and 30 Ezoic Placeholders on each page to get best results.
Ezoic will never display more ads than you want it to- you can change this setting in your Dashboard using the Max Ads Per Page App. It is best to leave this at 'Automatic'- the system will not display more ads than Google allows.
On pages with long content, sometimes the system will test with more than 5 ads per page - the additional ads will not be Google Ads, but ads from the many other networks we work with, like Criteo for example. Remember, the system is testing some pages with more ads and some with fewer; all the while measuring impact to user experience.