[Unity3D]　NavMeshAgentで目的地との距離を取得する正しい方法が知りたい。

提示コードのAI()関数部ですがvoid Start();関数部で最初の目的地を設定した後なぜかUpdate();関数内のAI();関数が呼ばれif()文の中身が実行されてしまいます。デバッグログを見ると目的地の距離が0が２４回Update()内で起きてるみたいなのですがこの場合どういった手法で目的地との距離を指定するのでしょうか？

######やりたいこと
目的地までの距離を得たい。

参考サイト: https://docs.unity3d.com/ja/2018.4/ScriptReference/AI.NavMeshAgent-destination.html
参考サイト: https://docs.unity3d.com/ja/2019.4/Manual/nav-AgentPatrol.html
参考サイト: https://docs.unity3d.com/ja/2018.4/ScriptReference/AI.NavMeshAgent-remainingDistance.html

cs
1using System.Collections;
2using System.Collections.Generic;
3using UnityEngine;
4using UnityEngine.AI;
5
6public class Tank_A : Enemy_Base
7{
8    private Vector3 attackVector;               //攻撃方向
9    private NavMeshAgent agent;                 //巡回
10    private int destPoint = 0;
11    [SerializeField] private Transform[] point; //巡回地点
12    [SerializeField] private GameObject bullet; //発射する弾
13
14
15
16    private void Awake()
17    {
18        
19    }
20
21    // Start is called before the first frame update
22    void Start()
23    {
24        agent = GetComponent<NavMeshAgent>();
25        agent.destination = point[destPoint].position;
26        //AI();
27    }
28
29    // Update is called once per frame
30    void Update()
31    {
32
33
34
35        AI();
36    }
37
38    private void FixedUpdate()
39    {
40        time += Time.deltaTime;
41
42
43        Debug.Log(agent.remainingDistance);
44    }
45
46
47    void AI()
48    {
49        if (agent.remainingDistance < 0.0001f)
50        {
51            //Debug.Log("あああ");
52            agent.destination = point[destPoint].position;
53            destPoint = (destPoint + 1) % point.Length;
54        }
55    }
56
57    public override void OnAttackAreaStay(Collider other)
58    {
59        if(other.gameObject.tag == "Player")
60        {
61            attackVector = other.gameObject.transform.position - transform.Find("Turret1").transform.Find("Main Gun1").transform.position;
62            transform.Find("Turret1").rotation = Quaternion.LookRotation(new Vector3(attackVector.x, 0, attackVector.z));
63            transform.Find("Turret1").transform.Find("Main Gun1").transform.rotation = Quaternion.LookRotation(attackVector);
64
65            if(time >= intervalTime || time == 0)
66            {
67                GameObject g = Instantiate(bullet, transform.Find("Turret1").transform.Find("Main Gun1").transform.position, 
68                    transform.Find("Turret1").transform.Find("Main Gun1").transform.rotation);
69                g.gameObject.GetComponent<Bullet>().moveVector = attackVector;
70
71                time = 0;
72            }
73        }
74
75
76    }
77
78
79    public override void OnAttackAreaExit(Collider other)
80    {
81        if (other.gameObject.tag == "Player")
82        {
83
84        }
85    }
86
87
88
89}
90