inheritance - problem setting class variable from external call

I am trying to implement sound detection for stealth in a game, but I can't seem to trigger an event in the Enemy's script that gives it the location of the sound/noise when the Player performs some action.
I have a variable _detectedAudio defined in a parent class base_entity (archetype for all Enemies) that is inherited by a class entity_keeper (specific Enemy) which is added to the Enemy GameObject in the Scene. From the Player's script, I am getting the Enemy GameObject's script as either base_entity (parent class) or entity_keeper (child class), and calling the base_entity function Register_AudioPoint(). When I typecast as base_entity, its showing that the function is being called and _detectedAudio's value has been changed. However when I try to access _detectedAudio in the Enemy's script entity_keeper while its running, its showing the old value, unchanged. When I tried typecasting as entity_keeper instead, it seems to work fine.

Player's script (base_player : MonoBehaviour):

 public void Walk()
 {
     // * testing walk noise alert
     Collider[] hitColliders = Physics.OverlapSphere(Position, MoveVector.magnitude * test_loudness);
     // Collider[] hitColliders = Physics.OverlapSphere(Position, test_loudness);
     for (int i = 0; i < hitColliders.Length; i++)
         if (hitColliders[i].gameObject.layer == game_variables.Instance.LayerEntity)
             // hitColliders[i].transform.GetComponent<base_entity>().Register_AudioPoint(transform.position);
             hitColliders[i].transform.GetComponent<entity_keeper>().Register_AudioPoint(transform.position);
             // Debug.Log(hitColliders[i].gameObject.name);
 }

Event function (base_entity : MonoBehaviour):

 public void Register_AudioPoint(Vector3 source)
 {
     // Debug.Log("heard");
     // AudioEvent event;
     // event.point = source;
     // event.intensity = 
     // _audioPoints.Add(source);
     // Debug.Log(Time.time + "\t" + _audioPoints.Count);
     
     // alert to nearest/loudest source
     // if (Vector3.Distance(source, transform.position) < Vector3.Distance(_detectedAudio, transform.position))
     // {
     _detectedAudio = source;
     _attentionTimer = _attentionTime;
         // Debug.Log("there~\t" + point);
     // }
 }

Enemy GameObject's script (entity_keeper : base_entity):

 protected override void State_Idle()
 {
     // alive...
     if (base_player.Instance.IsAlive)
     {
         // Debug.Log(_detectedAudio + "\t" + Vector3.Distance(_detectedAudio, player_motor.Instance.Position));
         // spotted...
         if (_detectedVision == player_motor.Instance.Position)
         {
             _positionMove = _detectedVision;
             // ...engage
             _state = State.ENGAGE;
         }
         // .!.heard... *borked
         // else if (_detectedAudio == player_motor.Instance.Position)
         else if (Vector3.Distance(_detectedAudio, player_motor.Instance.Position) < 1f)
         {
             _positionMove = _detectedAudio;
             // ...engage
             _state = State.ENGAGE;
         }
     }
     else
         // .!.keep moving|recite|struggle
         // _audio.Play("verse");
         _state = State.PATROL;
 }

I would prefer to be able to use the parent class typecast but I can't seem to get it to work. The only other alternatives I can think of are to either use tags to call each specific Enemy's script, since I don't have that many in the game (about 10-12). Or having an overriden version of Register_AudioPoint() in each of the child classes, but that'd be needlessly redundant. If anyone can suggest a solution or better alternative that'd be great.
Thanks in advance.