When configuring the mirror, I am able to set the HTTP Base URL, but I am not given the option to set the SSH Base URL. In the environment below, the clone URL's for the mirror are presented as:
HTTP: https://<username>@<bitbucket server URL>/bitbucket-mirror/scm/<project>/<repository>.git
SSH: ssh://git@<bitbucket server URL>:7999/<project>/<repository>.git
The HTTPS URL is correct, but the SSH URL is not configurable for the mirror as it is in the primary node.