As you have seen, global permissions are rather coarse in what they control and are applied globally. Since they can only be applied to groups, they are rather inflexible when it comes to deciding whom to grant permissions to.
To provide a more flexible way of managing and designing permissions, Jira allows you to manage permissions on a project level, which allows each project to have its own distinctive permission settings. Furthermore, permissions can be assigned to one of the following:
- Application access: This is for any user that has been granted access to the application
- Reporter: This is the user who submitted the issue
- Group: These are all users that belong to the specified group
- Single user: This is any user in Jira
- Project lead: This is the lead of the project
- Current assignee: This is the user currently assigned to the issue
- User custom field value...