ray cast direction callabration?

I have a 3d game start menu and in using 3dtext mesh for the options and on some devices (due to different resolutions im guessing) the ray seems to "aim low" as I need to touch above the textmesh to get a hit.

if (Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Began) {

             RaycastHit hit;
             Ray ray = Camera.main.ScreenPointToRay(Input.GetTouch(0).position);
             if (Physics.Raycast(ray,out hit))
             {
                 if (hit.collider.tag == "txt_Play")
                 {
                     PlayerPrefs.Save ();
                     Application.LoadLevel("Main");
                     
                     
                 }
                 
                 if (hit.collider.tag == "txt_Options")
                 {
                     if (sound==true)
                         
                     {    
                         sound = false ;
                         soundOption = 0;
                         PlayerPrefs.SetInt("SoundOption" , soundOption );
                         PlayerPrefs.Save ();
                         
                         Debug.Log ("sound is off");
                     }
                     else 
                     {
                         sound = true ;
                         soundOption = 1;
                         PlayerPrefs.SetInt("SoundOption" , soundOption );
                         PlayerPrefs.Save ();
                         Debug.Log ("sound is on");
                         
                     }
                     
                 }
             }
         }