I have a custom field "Field A" that is a single user picker field and shows users filtered on Active Directory security groups. Field Id is customfield_10373. Screenshot below:

Now I have created another Asset field called "Field B" in my People schema and referenced by "Employees" object and its fetching all the employee names etc. when used in a form. I want "Field B" to show filtered users like the ones shown in Field A and not all the employees when a user types in a user name in the field. How can I do that?
Tried doing this below but didn't work.
