Negative Volume

Not going to argue about things i cannot verify.

From the picture you posted back in December, it looks like the top surface is concave while the top is convex. If this was generated by intersecting with a Plane, at least on surface should appear flat. Since you can draw a straight line from the lower left edge to the upper right, I reasoned this to be part that was the water plane. The other line, assuming we see intersecting geometry here, exhibits a slightly convex form. Also the line along the middle of the top surface looks like the edge two joined symmetric surfaces and seems to transition to a isocurve at about the point where the surfaces touch.

I assumed and one should never do that. So the surfaces touch but do not intersect.