Question Problem with Stencil Buffer in Overlay Cutout Shader

I tried to use the Stencil Buffer for an Effect like this, but the other way around:

So I want to see a xor instead of an Intersection between the two objects.

Therefore I used this code in my Shader:

Code (CSharp):

1. Stencil{
2.                 Ref 0
3.                 Comp Equal
4.                 Pass IncrSat
5.             }

The Stencil Buffer is initialized with a 0 so the first time an object arrives at the pixel it should be drawn and the Buffer should increase to 1. The next time an object that uses the same shader checks the buffer and should fail the comparison. Therefore it should be discarded

So I try to use a single shader that solves the xor problem. But the effect is not like I want it to be:

Does someone know the solution for this problem?