GUI Healthbar not following the enemy

GUI to world position for GUI Button not working on landscape (Only works on portrait)

I'm making the healthbar for enemies.

The healthbar works and follows enemies very fine in portrait mode of Android phone. But when i convert it to landscape mode, the positions of healthbars aren't exactly on top of the enemies.

The healthbars still follow enemies, but their positions are e.g, 1-2 inches away from the enemies (Only happens in landscape mode).

For more info, i'm initiating the healthbar (GUI panel and a gui text inside it (not GUITexture)). And while i initiate it, i'm making it the child of my canvas.

Here's my code,

 void Update () {
     Vector2 targetPos = Camera.main.WorldToScreenPoint (Enemy.transform.position);
     EnemyHealthBar.transform.position = targetPos;
 }