Making a singing bowl sing in VR, responding to incoming angle

I have the model, the looping audio tracks, and velocity-responsive audio script, but no good solution.

Ideally, I would like a VR controller to be able to tap the side of a singing bowl to play one sound, and trace along the side for the looping resonant sound (like tracing your finger along the rim of a wine glass). The velocity of the hit would change the volume, not the track.

Bonus question! Then there's the problem of the concave collider. I can make a sphere collider for now, but if I wanted to be thorough and place a hundred tiny box colliders along the sides so it can't sound in the center, how would I keep a continuous sound, with the script in each one? Or should I give up on that part?

Current script below. Senses velocity of impact and switches the audio clip with a higher speed. I need to switch 'relative velocity' to 'angle of impact < 45' angle.'

 public class sfxBowlHit2 : MonoBehaviour {
 
     public AudioClip hitDirect;
     public AudioClip hitSlide;
 
 
     private AudioSource source;
     private float velToVol = .25F; // Louder volume when hit with higher velocity
     private float velocityClipSplit = 10F; // Switch audio clip once reaching this threshold
 
 
     void Awake () {
         source = GetComponent<AudioSource>();
     }
         
     void OnColliderEnter (Collision coll) //coll is a standard Unity variable
     {
         float hitVol = coll.relativeVelocity.magnitude * velToVol;  // Louder volume when hit with higher velocity
         if (coll.relativeVelocity.magnitude < velocityClipSplit)    // Need to adapt this from velocity to angle of impact
             source.PlayOneShot(hitDirect,hitVol);        
         else 
             source.PlayOneShot(hitSlide,hitVol);
     }
 }