Pull Request 'Reviewers' not auto-populating from JIRA issue Watchers

I have JIRA 6.1.2, and Stash 2.8.1 with StoryFlow 1.0.1 installed. All of the other StoryFlow features (auto issue transition, auto pull request links created in JIRA issues, etc) work, however, when I create a pull request, the Reviewers are not automatically populated from JIRA watchers. Is there something else I need to configure to get this working?