My intuition says that with vertical walls, the problem collapses to 2d, but that 2d is a cross section of a 3d shape, and an infinite number of 3d shapes can h

My intuition says that with vertical walls, the problem collapses to 2d, but that 2d is a cross section of a 3d shape, and an infinite number of 3d shapes can hold that as the max cross section envelope.