Curiosity Question Authorization Checks

I created a Supervisor role that had only CO13, I wanted to use this role with other roles in place that have the plant numbers.  So for the field WERKS I entered ' ' on role A below. Then Role B has the plant numbers on field WERKS, that work as planned. The problem came under the ACTVT field.  Role A has activity 85, Role B has 01.02 and 03 assigned.  The authorization failed, I had to add 85 to the ACTVY for Role B.  Why didn't pick up the 85 on the ACTVY field from Role A if both roles were asigned to the user?

Thanks for your help

TS