Problem with GUI element following enemy

Hello guys I'm experiencing a little problem while setting a ui element to follow the enemies. Basically the UI object moves with the enemy , but the movement is based on the position of the camera and on the PoV. If the enemy is in the middle of the screen the button is centered, but if the enemy is on the right the button is on the left and if it's on the left, the button is on the right. Notice I'm just talking about the x, the y is fine

enemy on the right of the camera:

enemy on the left of the camera:

and this is the code I'm using:

 Vector3 screenPos = Camera.main.WorldToScreenPoint(unit.transform);
 button.tranform.position = screenPos;

thanks a lot