Trying to understand auditing roles

Oracle = 12.1.0.2.180417, Linux.

I am setting up an audit policy to audit everything that happens when someone is connected using that role.

The audit policy is defined as:

CREATE AUDIT POLICY dbawtf ROLES mydbas;

The audit policy correctly audits users in the "mydbas" role, but also audit every other user even if they are not assigned the "mydbas" role.

My understanding is that only the users using the "mydbas" role would be audited. 

So I am sure I am misunderstanding how role based auditing is supposed to work.  Can somebody point me to a clear example of auditing for a role?