I think the discrepancy is due to what's described in Email Performance Report & Analytics (Using new program/email for each send) – Welcome to the Digesto community!
Your 2% benchmark is probably wrong (which is a good news in some way ). This is due to Digesto resending the same email over and over, which skews the metrics. There is an entire discussion on the community about that - in a nutshell - a lead opening the same email twice will never count as a 2 opens. So your 2% only reflects first time Newsletter Opens.
We've released an improvement 2 years ago that fixes this issue, by starting each send from a new email, your account was created prior to that and it has not been activated.
Feel free to connect with our support and we'll be happy to help you turn this on in your account.