OnBecomeVisible is not working the way i want?

I am working on a horror game project. What i want to do is killing player if enemy is visible and close to player. But on OnbecomeVisible is not working if enemies all body is not in frame. If i can't see enemies foot onbecomevisible doesn't work. How can i fix this. I want this death screen to work if a certain part of the enemy is visible too.

  `using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class DeathHandler : MonoBehaviour
 {
     //config params
     [SerializeField] Canvas DeathUI;
 
     [SerializeField] GameObject AnimatedImage;
 
     [SerializeField] GameObject DeathCam;
 
     [SerializeField] GameObject Player;
 
     [SerializeField] GameObject StaticSound;
 
     [SerializeField] float DeathDistance = 2.1f;
 
     //params
     float DistanceBetweenEnemy;
 
     // Start is called before the first frame update
     void Start()
     {
         DeathUI.enabled = false;
     }
 
     // Update is called once per frame
     void Update()
     {
        CheckforDistance();
     }
 
    IEnumerator DeathScreen() 
     {
         AnimatedImage.SetActive(true);
 
         Player.SetActive(false);
 
         DeathCam.SetActive(true);
 
         StaticSound.SetActive(true);
 
         StaticSound.GetComponent<AudioSource>().Play();
 
         yield return new WaitForSeconds(4.0f);
 
         StaticSound.GetComponent<AudioSource>().Stop();
 
         HandleDeath();
     }
 
     public void HandleDeath() //used as string reference
     {
         Time.timeScale = 0;
 
         DeathUI.enabled = true;
 
         Cursor.lockState = CursorLockMode.None;
 
         Cursor.visible = true;
     }
 
     private void CheckforDistance() 
     {
         DistanceBetweenEnemy=  Vector3.Distance(FindObjectOfType<EnemyAI>().transform.position, transform.position);
 
         if(DistanceBetweenEnemy<DeathDistance && FindObjectOfType<EnemySpawner>().isEnemyVisible) 
         {
             StartCoroutine(DeathScreen());
         }
     }
   `