Old post, but I followed this video and was successfully able to fix the post process depth issue without adding an ocean body to the scene. Specifically around the 5:30 mark. Let's Build the RPG! - 16 - Unreal Engine 5 Water System Beginner Tutorial - Lakes and Rivers - YouTube
Changing the Channel Depth seems to increase the post process depth.
Side note: Your landscape seems to need “Enable Edit Layers” checked for this value to dynamically edit the landscape geometry.