How to Make the Camera to Cull According to a Oblique Matrix?

I am making a reflection camera that is used for a flat water surface. I have successfully made the camera to render objects that are only above the water surface with:

Code (CSharp):

1. camera.CalculateObliqueMatrix()

However, although objects that are under the water surface are not being rendered, they are still issuing draw calls when they are within the camera's frustum. I tried to set:

Code (CSharp):

1. camera.cullingMatrix = obliqueMatrix * camera.worldToCameraMatrix;

but this doesn't work. How do you make the camera to calculate rather or not to issue draw call according to the new obliqueMatrix?

 

Stuck on the same issue for a while now, long enough to engage in some thread necromancy. Did you ever get this solved?

Here is a related question from 2017 and I'm experiencing the same issue.
https://answers.unity.com/questions/1300080/calculating-an-oblique-clipping-matrix-making-occl.html

Thanks for any insights!