Moving object on plane

Good day!

Please help with locked moving object on plane. Exist object A on plane B. He moving repeatly from one side of palne to another. I make mathematical calculations to get left and right cordinates of plane B and object A. If plane B scale more than 3 - begin troubles. Object A just moving to the end of plane and fall. In debug log i can see than coords of object A less than plane B.

Here what i mean:

Here code: using UnityEngine; using System.Collections;

 public class Enemy : MonoBehaviour {
     private float PlaneSizeX = 64;
     private float EnemySizeX = 64;
     private float eLeft; //enemy left position
 
     private float pLeft; //plane left position
     private float pRight; //plane right position
     private float Speed = 1;
     private Rigidbody2D mBody;
     private bool grounded = false;
 
     // Use this for initialization
     void Start () {
         mBody = GetComponent<Rigidbody2D>();
         eLeft = EnemySizeX * mBody.transform.localScale.x;
         eLeft = -(eLeft / 2) + (mBody.transform.position.x * EnemySizeX / 2);
         Debug.Log ("Enemy x : " + eLeft + " " + (eLeft + EnemySizeX * mBody.transform.localScale.x));
     }
     
     // Update is called once per frame
     void Update () {
         eLeft = mBody.transform.position.x * EnemySizeX - (EnemySizeX / 2);
         //eRight = mBody.transform.position.x * EnemySizeX + (EnemySizeX / 2);
         if (grounded) {
             //right test
             if ((eLeft + EnemySizeX * mBody.transform.localScale.x) >= pRight) {
                 Debug.Log ((eLeft + EnemySizeX * mBody.transform.localScale.x) + " >= " + pRight);
                 Speed = 0;
             }
             //left test 
             //if (eLeft <= pLeft)  {
             //    Speed = 1;
             //}
         }
         mBody.velocity = new Vector2(Speed, 0);
         Debug.Log (eLeft + " " + (eLeft + EnemySizeX*mBody.transform.localScale.x) + " " + mBody.transform.localScale.x);
     }
 
     void OnCollisionStay2D(Collision2D coll)
     {
         grounded = true;
         Collider2D Plane = coll.gameObject.GetComponent<Collider2D> ();
         //pLeft = (Plane.transform.position.x * PlaneSizeX - (PlaneSizeX / 2)) * Plane.transform.localScale.x;
         //pRight = (Plane.transform.position.x * PlaneSizeX + (PlaneSizeX / 2)) * Plane.transform.localScale.x;
         float ScaledSize = PlaneSizeX * Plane.transform.localScale.x;
         pLeft = -(ScaledSize)/2 + (Plane.transform.position.x * PlaneSizeX/2);
         pRight = (ScaledSize)/2 + (Plane.transform.position.x * PlaneSizeX/2);
         Debug.Log("Plane x: " + pLeft + " " + pRight);
     }
 }