Case where F4 help restriction wasn't working, OrgUnit was used as Nav attribute of another master data object.
As a workaround, we baked in OrgUnit in underlying DSO by master data look up and then in Multiprovider level we assigned this direct object from to Nav Attr OrgUnit of master data.
So that no query changes were made.
But surprisingly this time F4 help restriction is now working with same object (Nav Attr), may be because in Multiprov its assigned to direct OrgUnit of DSO.