Changing resolution affect camera width but not height

Hi everybody !

I need to know the width and height of my camera because i want to place some GameObject at a point from the camera border. I made many research and many people says that i could obtain these information with this code :

     Camera cam = GameObject.FindGameObjectWithTag("MainCamera").GetComponent<Camera>();
     float vertExtent = cam.orthographicSize;
     float horzExtent = vertExtent * Screen.width / Screen.height;
     float cameraWidth = horzExtent * 2;
     float cameraHeight = vertExtent * 2;
     print("taille de la camera H : " + cameraWidth + " V = " + cameraHeight);

But this code doesn't give me the same results for the width when i change the game's resolution ( but the height stay the same ! )

Can someone explain me why and maybe give me a solution for getting the same camera width when I change resolution ?

Thanks in advance