CalculateFrustunPlanes / TestPlanesAABB returns unexpected results

I'm trying to figure out how to bind a camera to a viewable area.

The camera is orthographic and rotated to (30,45,0) for an isometric view.

The camera is a child of an unscaled gameobject with no rotation (this parent is used to control position easily).

When I generate planes using the manual's example of CalculateFrustumPlanes, the planes are all over the place.

I need the functionality to work with different orthographic sizes as that will be used to zoom the camera.

If I use the below code to check if a collider is within the frustum I get erroneous results (see image).

     bool doOnce = true;
     public Collider[] toDetect;
     private Plane[] planes;
     string detected = "";
     void HandlePanBounds()
     {   
         if (doOnce)
         {
             doOnce = false;
             /*
             int i = 0;
             while (i < planes.Length)
             {
                 GameObject p = GameObject.CreatePrimitive(PrimitiveType.Plane);
                 p.name = "Plane " + i.ToString();
                 p.transform.position = -planes[i].normal * planes[i].distance;
                 p.transform.rotation = Quaternion.FromToRotation(Vector3.up, planes[i].normal);
                 i++;
             }
             */
         }
         Plane[] planes = GeometryUtility.CalculateFrustumPlanes(Camera.main);
         detected = "nothing";
         for (int i = 0; i < toDetect.Length; i++)
         {
             if (GeometryUtility.TestPlanesAABB(planes, toDetect[i].bounds))
             {
                 detected = toDetect[i].gameObject.name;
             }
         }
     }
 
 
     void OnGUI()
     {
         GUI.Box(new Rect(0, 0, 100, 100), "Detected: " + detected);
     }

HandlePanBounds() is called in Update().

All help is appreciated. I've Googled this and tried a variety of answers for the past 2+ hours and they aren't getting me anywhere.