Thank you for sharing this with the community! I opened up your sandcastle demo and noticed some very odd behavior. It seems like parts of the terrain are appearing near the blue box entity that you added. Just so that I am clear - what is your goal with this project?
I want to achieve water reflection in post processing. I try to use Ray Marching in Eye Space.（I can only describe it briefly. My English is not very good）
I do not think our API currently provides an easy way to implement water reflections in post-processing. I currently do not have a timeline for when this will be implemented. However, I did find this community forum thread that partially addresses this topic.