How to use position hierarchy for multiple employees at one position?

We are in phase of planning position hierarchy for our organization.

If we have a parent position (A) with multiple headcounts at child position (lets say B & C are employees at child position). When further grand child position to be tagged to this position (for example new employee reports to B) how would we define position hierarchy to specify that this employee reports to B but not C, who is also an incumbent of the same position?

Please clarify/ suggest how to implement this requirement in position hierarchy, given that we are not expecting to implement new position for each employee.