weird Skin width problem with raycast collision

Hello everyone, am trying to check for collision using raycast but am facing a very weird problem and i don't know how to solve it, the collision works perfectly when the skin width (distance between ray origin and hit point) is bigger than 0.5 but in that case the object stops before it actually hit something, and when i reduce the distance i had this very strange behavior, sometimes it works and sometimes it didn't i uploaded a youtube video here i also uploaded the game package here

and finally here is all the code i use to make the box move and collide :

 using UnityEngine;
 using System.Collections;
 
 public class J2PlayerMovement : MonoBehaviour
 {
     
     
     public float         speed ;             // speed
     public float         ySpeed, yDir;         // Y direction & x speed 
     public float         xSpeed, xDir;        // X direction & x speed 
     public float         maxDist ;            // max distance between ray origin and hit point 
     private RaycastHit     hit ;
     private Transform     myTransform;
     float tmpYdir,tmpXdir;
     [HideInInspector]
     public Vector3 myPos;
     
     void Start ()
     {
     
         myTransform = transform;
         myPos = myTransform.position;
         ySpeed = xSpeed = speed;
         tmpYdir=tmpXdir=0;
     }
     
 void Update ()
     {
         //set the directions 
         xDir = Input.GetAxisRaw ("Horizontal");
         yDir = Input.GetAxisRaw ("Vertical");
         //save the last direction
         if(yDir!=0){
             tmpYdir=yDir;
         }
         if(xDir!=0){
             tmpXdir=xDir;
         }
         //check for collision
         collision ();
         //move up down
         myPos.y += (ySpeed * yDir) * Time.deltaTime;
         //move left right 
         myPos.x += (xSpeed * xDir) * Time.deltaTime;
         //apply 
         myTransform.position = myPos;
         
         /**Note : i changed the order and the resulst is always the same **/
     }
     //check for collision 
     void collision ()
     {
         //set the Y speed to the default speed value
         ySpeed = speed;
         //make 3 rays upon/under the object 
         for (int i = -1; i<2; i++) {
             //set ray setting 
             Ray ray = new Ray (
                 new Vector3 (
                         myTransform.position.x + myTransform.localScale.x / 2 * i,
                          myTransform.position.y + (1 * Mathf.Sign (tmpYdir) * myTransform.localScale.y / 2), 0), 
                         new Vector3 (0, Mathf.Sign (tmpYdir), 0)
                 );  
             //check if one of those rays hit something
             if (Physics.Raycast (ray, out hit, Mathf.Abs (tmpYdir) + maxDist)) {
                 //calculate the distance between ray origin and the hit point 
                 float dist = Vector3.Distance (ray.origin, hit.point);
                 Debug.DrawRay (ray.origin, ray.direction, Color.yellow);
                 //if distance reach the limit 
                 if (dist <= maxDist) {
                     //stop moving 
                     ySpeed = 0;
                     Debug.DrawRay (ray.origin, ray.direction, Color.red);
                 }
                 
             } 
             //if you're not touching anything 
             else {
                 Debug.DrawRay (ray.origin, ray.direction, Color.green);
             }
         }
     
         /*********************************/
         /*SAME ABOVE PRINCIPLE FOR THE 2 OTHER DIRECTIONS*/
         
         /*********************************/
         
         xSpeed = speed;
         for (int i = -1; i<2; i++) {
             Ray ray = new Ray (
                 new Vector3 (
                         myTransform.position.x + (1 * Mathf.Sign (tmpXdir) * myTransform.localScale.x / 2),
                          myTransform.position.y + myTransform.localScale.y / 2 * i, 0), 
                         new Vector3 (Mathf.Sign (tmpXdir), 0, 0)
                 );  
             if (Physics.Raycast (ray, out hit, Mathf.Abs (tmpXdir) + maxDist)) {
                 float dist = Vector3.Distance (ray.origin, hit.point);
                 Debug.DrawRay (ray.origin, ray.direction, Color.yellow);
                 if (dist <= maxDist) {
                     xSpeed = 0;
                     print ("xx");
                     Debug.DrawRay (ray.origin, ray.direction, Color.red);
                 } 
             } else {
                 Debug.DrawRay (ray.origin, ray.direction, Color.green);
             }
         }
     }
 }