how to update access level for secondary managers

Summary:

How to make access level to 'no update allowed' for secondary managers ?

Content (please ensure you mask any confidential information):

In administer worker, under 'Status & Hierarchy' there is a section 'Plan Access' where we can update the access to secondary managers.

When I update the access level for secondary level :

But when I try to do Act As proxy with the secondary manager, I still see that the secondary plan is 'updates allowed' :

I even tried to update the access directly in the Plan Access page and put the access level for secondary hierarchy to 'no access' but the access is not updated properly :