How to limit access to one specific task on a custom security role

We have users who need to have access to a specific task. NOT the entire Setup & Maintenance. I have assigned a privilege for what I think is the correct task but it is not accessible. In the R12 world, this is done with custom menus assigned to custom responsibilities. Tried to do the same in Cloud financials but to no avail.

Specifically - I want via a custom security role to allow Grant users not only to be able to edit and define grants but also to be able to input sponsor information via the "Manage Sponsor" task and screens. Again, Assigning the "Manage Sponsors" privilege is not sufficient it seems.