The coverage feature will only send calls to the mailbox of the originally called extension, ie, the extension that is assigned the coverage path. To do this, the Audix hunt group is assigned as the last coverage point in the coverage path.
If you want the call to go to another extension’s mailbox, you will have the send the call to a coverage path which has a VDN as the last coverage point. The respective vector has the messaging step pointing to the mailbox (e.g. 2070) you desire.
Hope this helps.