Enemies spawn on top of each other(C#)(Unity)

Good day, i'm having an issue with an enemy random spawner code. problem is that i got two enemies but when they spawn sometimes they spawn on top of each others. some1 know how to fix it? here is code:

  using System.Collections;
  using System.Collections.Generic;
  using UnityEngine;

  public class EnemySpawner : MonoBehaviour
  {
 public GameObject Enemy;
 public GameObject Enemy2;
 float maxSpawnRateInSeconds = 5f;
 void SpawnEnemy()
 {
     Vector2 min = Camera.main.ViewportToWorldPoint (new Vector2 (0, 0));

     Vector2 max = Camera.main.ViewportToWorldPoint (new Vector2 (1, 1));

    GameObject anEnemy = (GameObject)Instantiate (Enemy);
     anEnemy.transform.position = new Vector2 (Random.Range (min.x, max.x), max.y);

    GameObject anEnemy2 = (GameObject)Instantiate (Enemy2);
     anEnemy2.transform.position = new Vector2 (Random.Range (min.x, max.x), max.y);

     ScheduleNextEnemySpawn();
 }
 void ScheduleNextEnemySpawn ()
 {
     float spawnInNSeconds;

     if(maxSpawnRateInSeconds > 1f)
     {
         spawnInNSeconds = Random.Range(1f, maxSpawnRateInSeconds);
     }
     else
         spawnInNSeconds = 1f;
     Invoke ("SpawnEnemy", spawnInNSeconds);
 }

 void IncreaseSpawnRate()
 {
       if(maxSpawnRateInSeconds > 1f)
            maxSpawnRateInSeconds--;

    if(maxSpawnRateInSeconds == 1f)
     CancelInvoke("IncreaseSpawnRate");
     }

    public void ScheduleEnemySpawner()
    {
      maxSpawnRateInSeconds = 5f;

      Invoke ("SpawnEnemy", maxSpawnRateInSeconds);   

   InvokeRepeating ("IncreaseSpawnRate", 0f, 30f);
  }
    public void UnscheduleEnemySpawner()
    {
      CancelInvoke("SpawnEnemy");
      CancelInvoke("IncreaseSpawnRate");
    }
  }