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 the permissions to.
To provide a more flexible way of managing and designing permissions, JIRA allows you to manage permissions at the project level, which allows each project to have its own distinctive permission settings. Furthermore, permissions can be assigned to one of the following:
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: This user is specified in a custom field of the type User Custom Field
Project role: These are all users that belong to the specified role
Group custom field value: These are users within the...
