zoom problem with GUI Box that follows a character

I have a GUI box following a sprite character in a 2d Top Down Game. If I zoom in, the GUI box goes up, if I zoom out, the GUI box moves down, instead of staying at the point it was drawn at game start. Have a look at the image below.

Some more details:

• the camera is in orthographic mode (although the same happens in perspective mode)

• the camera zoom is done by changing its OrthographicSize-value

This is the code I use to draw the GUI:

 void OnGUI()
 {
         GUI.skin = guiSkin;
 
         boxPosition = Camera.main.WorldToScreenPoint(baseAgent.transform.position);
             
         guiSkin.box.fontSize = fontSize;
 
         nameLabelText = baseAgent.name;

         Vector2 content = guiSkin.box.CalcSize(new GUIContent(nameLabelText));
 
         Vector3 boxPosition = new Vector3(Mathf.Clamp(boxPosition.x, 0 + (content.x / 2), Screen.width - (content.x / 2)),
             Mathf.Clamp(boxPosition.y, 40, Screen.height), boxPosition.y);
 
         GUILayout.BeginArea(new Rect((boxPosition.x + offsetX) - (content.x / 2), (Screen.height - boxPosition.y) + offsetY, content.x, content.y));
         GUILayout.BeginHorizontal();
 
         GUILayout.Box(nameLabelText);

         GUILayout.EndHorizontal();
         GUILayout.EndArea();
         
     }

Any clue on what might solve the issue would be greatly appreciated! Thanks!