Attached is my latest simple test(minus the cached bgeos to save size), a torus falling into a narrow Flip tank. I am satisfied with the level of detail and Particle Separation. I am using a Feedback Scale of 1.0 in my Solver.

What is wrong is after the torus penetrates the water surface it exits the side or back of the FLIP tank and then accelerates down. The FLIP tank fails to contain the torus.

Are there settings somewhere in the FLIP tank solver that will make it function as a container with collision to any objects dropped inside?