Determining Plane's UV under the cursor

Hi!
I have a plane object. This plane is fixed relative to camera (plane is camera's child and always facing the camera -- image attached). This plane has some RenderTexture on it. Now I want to know, what UV coordinate is currently under the mouse cursor.
The following script is sitting on this plane object:

Code (CSharp):

1.  
2.  
3. //....
4. _collider = gameObject.GetComponent<Collider>(); // Plane's mesh collider
5. //....
6.  
7.  
8. void FixedUpdate()
9.         {
10.             RaycastHit hit;
11.  
12.             var p = UnityEngine.Input.mousePosition;
13.  
14.             if (_collider.Raycast(Camera.main.ScreenPointToRay(p), out hit, 100f))
15.             {
16.                 var meshCollider = hit.collider as MeshCollider;
17.                 var rend = hit.collider.GetComponent<Renderer>();
18.  
19.                 if (rend == null || rend.sharedMaterial == null || rend.sharedMaterial.mainTexture == null || meshCollider == null)
20.                     return;
21.  
22.                 var pixelUV = hit.textureCoord;
23.  
24.                 pixelUV.x *= rend.material.mainTexture.width;
25.                 pixelUV.y *= rend.material.mainTexture.height;
26.  
27.                 Debug.Log("UV=[" + hit.textureCoord.x + ";" + hit.textureCoord.y + "]" + ", XY=[" + pixelUV.x + ";" + pixelUV.y + "]");
28.             }
29.         }

But coordinates I see in the log are very strange. First of all, when I change aspect ratio in a viewport, point that had XY[51,466] in 16:10 becomes XY[95,464] in 4:3 and so on. Secondly, offset is so huge that I am getting UV readings even if mouse pointer is nowhere near this plane.

How to correctly get these UV readings regardless of screen size?

 

UPD: I ended up ditching mouse pointer entirely. Code above actually works well if you hide cursor and just look at the collision detection. Now I am showing a really small sphere at the ray hit point, and when you move your mouse, this sphere smoothly follows plane surface: now this is my "pointer". It works really well, and even better than "real" pointer: my 3d-cursor actually follows object geometry. And as this sphere represent actual raycast hit point, precision is great.

I really like this workaround, but question is still open.