Change the Layer of Colliders in specific portion of Viewport

Greetings. I am attempting to make it so that all objects in the bottom right of the viewport are placed on the "Ignore Raycast" layer. However, I have had difficulty finding success in this endeavor; my code is as follows:

         Camera cam = (Camera)FindObjectOfType(typeof(Camera));
         Vector3 gtPos = GameObject.FindGameObjectWithTag ("GT").transform.position;
         Vector3 gtScreenPos = cam.WorldToViewportPoint(gtPos);
         Vector3 pos = cam.ViewportToWorldPoint(new Vector3(Screen.width,0,gtScreenPos.z));
         
         nearbyColliders = Physics.OverlapSphere(pos,10);
         foreach (Collider c in nearbyColliders)
         {
             c.gameObject.layer = LayerMask.NameToLayer("Ignore Raycast");
         }

I am unsure as to what I might be doing wrong. Any help would be greatly appreciated.