how to fire a missile that select nearest enemy to my aim

I have a lot of enemy , when I fire I don't know how can I chose right target for missile , I test nearest enemy but its not ok! (if the enemy was behind of player the missile chose it) The missile must chose nearest enemy to my aim ( center of view ) This is my script , who can I do that

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 
 
 public class Missile : MonoBehaviour
 {
     public float missileVelocity = 100f;
     public float turn = 20f;
     public Rigidbody homingMissile;
     public float fuseDelay;
     public GameObject missileMod;
     public ParticleSystem SmokePrefab;
     public AudioClip missileClip;
     public Transform Enemy;
 
 
     private Transform target;
     // Use this for initialization
     void Start()
     {
 
         var closestGameObject = GameObject.FindGameObjectsWithTag("Enemy").OrderBy(go => Vector3.Distance(go.transform.position, transform.position)).FirstOrDefault();
         float dist = Vector3.Distance(closestGameObject.transform.position, transform.position);
         Debug.Log(closestGameObject);
         //Fire();
 
     }
 
     // Update is called once per frame
     void FixedUpdate()
     {
         if (target == null || homingMissile == null)
             return;
 
         homingMissile.velocity = transform.forward * missileVelocity;
 
         Quaternion targetRotation = Quaternion.LookRotation(target.position - transform.position);
 
         homingMissile.MoveRotation(Quaternion.RotateTowards(transform.rotation, targetRotation, turn));
     }
 
     void Fire()
     {
         Start(); 
         //StartCoroutine(fire());
     }
 
 
     void OnCollisionEnter(Collision theCollision)
     {
         StartCoroutine(oncollision());
     }
 
     IEnumerator fire()
     {
         yield return new WaitForSeconds(fuseDelay);
         AudioSource.PlayClipAtPoint(missileClip, transform.position);
 
         float distance = Mathf.Infinity;
 
         foreach (GameObject go in GameObject.FindGameObjectsWithTag("Enemy"))
         {
             float diff = (go.transform.position - transform.position).sqrMagnitude;
 
             if (diff < distance)
             {
                 distance = diff;
                 target = go.transform;
             }
         }
     }
 
     IEnumerator oncollision()
     {
         SmokePrefab.emissionRate = 0.0f;
         Destroy(missileMod.gameObject);
         yield return new WaitForSeconds(5);
         Destroy(gameObject);
     }
 
 
 }