mathematics – How to project a Matcap correctly in Amplify Shader Editor

Unity’s Amplify Shader Editor comes with an example of matcap nodes setup, however, the matcap projection in this example is incorrect.
As you can see the texture becomes distorted when it’s on de edges of the screen, that shouldn’t happen with a correct matcap:

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On the secoud image, this is how a matcap should look, without major distortions.

Does any expert in shaders knows the right way to project a matcap using the nodes? I’ve done my search and there is absolutelly no information about this around the internet, any response would add for this Shader documentation.
I’m extremelly in need that matcap works with this shader.