Unable to track SES/SNS Open events by recipient

I am processing SES events with a lambda that receives the events via an SNS topic that is a destination for a configuration set. I have no problems receiving Send, Delivery, Bounce, Open and so on. My use case sends emails to a single address, with a bcc to a second address. My problem is I don't see a way of distinguishing the recipients for an Open event. By contrast, it is straightforward to distinguish the recipients for a Delivery event. In that case the SNS JSON event payload has a "delivery" key that contains a "recipients" array that lists the email addresses delivered to. In my case, two Delivered events, one for the "to" address and one for the "bcc" address. Perfect. For the "Open" event there is a corresponding "open" key in the payload. But it doesn't seem helpful. It contains a timestamp, a userAgent and an ipAddress. I don't know what the ipAddress refers to, but whatever it is, it seems unlikely to provide a robust way of determining which recipient opened the email. Can anyone help me figure out which recipient opened the email? TIA.