Spawning enemies at an offset

I have fixed spawn locations in my game and I would like to spawn my enemies within a range close to the spawn point, rather then the enemies coming straight from the one fixed point if you get me.

Is there a way I can do that with my current setup?

 using UnityEngine;
 using System.Collections;
 
 public class spawnBall : MonoBehaviour 
 {
     //The spawn points for the enemies
     Vector3[] spawnPoints;
 
     //Initialises the end of the array for the enemies
     int endOfArray;
 
     //The wait time before the coroutine will start
     private int timeToBegin = 2;
     
     //Determines the spawn time of the enemies
     private float spawnTime = 2;
     
     //The object spawned towards the enemy
     public GameObject[] randomBall;
 
     void Start()
     {
 
         //Finds all ovjects marked with the tag Spawn Points
         GameObject[] objs = GameObject.FindGameObjectsWithTag("SpawnPoints") as GameObject[] ;
         
         //Sets the spawnPoints varibale to the size of the objs array
         spawnPoints = new Vector3[objs.Length] ;
         
         //for loop which trasfers all data into the array
         for(int i = 0 ; i < objs.Length ; i++)
         {
             spawnPoints[i] = objs[i].transform.position ;
         }
         //sets the end point for the array
         endOfArray = spawnPoints.Length;
         
         //Starts the coroutines for the enemies and missiles
         StartCoroutine(Spawn());
 
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     //Instantiates a new enemy based on a time given by the players score
     IEnumerator Spawn()
     {
 
 
         yield return new WaitForSeconds(timeToBegin);
         while (true)
         {
             int prefeb_num = Random.Range(0,15);
              //I'd like to create the offset here on the x-axis
             Instantiate(randomBall[prefeb_num], spawnPoints[Random.Range(0,endOfArray)], Quaternion.identity);
             yield return new WaitForSeconds(spawnTime);
         }
     }
 
     void OnGUI()
     {
         GUI.Label(new Rect(10, 10, 100, 100), "FPS: " + (int)(1.0f / Time.smoothDeltaTime));        
     }
 
 
 }