Are you referring to placeholders that are title 'ai_placeholder' ? Those are specifically generated for mobile devices typically, and would help with the mobile setup when other ad placeholders aren't optimized for those screen sizes.
They'd adjust based on any CSS exclusions you setup however - but if you can explain what about them you're attempting to edit, we can clarify / provide further assistance.
Do you have an example URL where you're seeing the unnatural concentration you're describing? Is it on mobile, or desktop devices?
Just as an aside - it's really important to keep in mind that the setup is being tested consistently, especially at the outset of monetization services through Ezoic. What you're seeing is most likely not what other users are seeing - and often publishers will see a more dense / concentrated setup than the average user: https://support.ezoic.com/kb/article/im-worried-that-im-seeing-too-many-ads-on-my-site