You can troubleshoot ePMV changes via the guides available on the topic at support.ezoic.com --- just search 'epmv' there 🙂
If you believe AdSense would perform better, you'd just need to make sure Mediation is enabled. If AdSense Mediation is connected, AdSense can bid against the Ezoic partners and if they're willing to pay more for an ad location, their ads show 🙂