Does the speed of the object depends on target distance while using vector3.movetowards()

I am trying to make a Piano Tiles type game in unity. So I have 6 empty gameobjects(targetGrid[0-5]) which are the targets of my tiles. I am sending my first tiles to first target[0], after reaching targetGrid[0] I'm making the new target to targetGrid1 and so on.

But the problem is the speed of my tile is slower from targetGrid[0]-targetGrid1 than the others like:

speedOf targetGrid[1-2] = speedOf targetGrid[2-3] = speedOf targetGrid[3-4] = speedOf targetGrid[4-5] is greater than speedOftargetGrid[0-1]

Here is the video of the problem : https://www.youtube.com/watch?v=20pwdbaw0aQ

here is the project package :

Why is that ?? And how can i solve this problem.

Here is my code and screenShot: public List gridPos = new List ();

 //public bool middleCrossed = false;

 //public CollectableTypes collectableTypes;

 public CollectibleManager collectableManager;
 private int currentGridNo = 0;

 // Use this for initialization
 void Start () {
     transform.position = new Vector3 (gridPos[0].position.x,gridPos[0].position.y);
 }

 // Update is called once per frame
 void Update () {
     if(currentGridNo<5)
         transform.position = Vector3.MoveTowards (transform.position, gridPos [currentGridNo+1].position, collectableManager.collectable_speed*Time.deltaTime);
     if (transform.position == gridPos [Mathf.Clamp((currentGridNo+1),0,5)].position) {
         if (currentGridNo < 5) {
             Debug.Log ("calling " + currentGridNo + " Grid");
             MakeNextObjectGo ();
         }
         else {
             Debug.Log ("calling ManagerFunction");
             currentGridNo = 0;
             transform.position = new Vector3 (gridPos[currentGridNo].position.x, gridPos[currentGridNo].position.y);
         }
     }


 }

 public void MakeNextObjectGo()
 {
     currentGridNo++;
     collectableManager.WhichGridCrossedGridCrossed (transform);
 }

 public void StartAgain()
 {
     collectableManager.FinishedMoving (transform);
 }

}