One more brief comment:
As to where the extra water came from, the Bible itself refers to its sources: "all the fountains of the deep burst forth, and the windows of the heavens were opened." (Gen.7:11). The atmosphere would not have provided sufficient rain for a massive global Flood.
Yes, the Bible cites two sources for the floodwaters. For liberals, both sources have mythological overtones. The "windows of heaven" alludes to the cosmic sea above the solid dome of the sky while the "fountains of the deep" refers to the primordial abyss.
For conservatives, the "windows of heaven" is a figurative expression for rainclouds and rainwater.
But what about the "fountains of the deep"? Some say that's poetic. Some think that refers to subterranean water. Speaking for myself:
i) The parallelism in Gen 7:11 makes the general point that the deluge had two sources: water above and water below.
ii) "Fountains of the deep" is a poetic synonym for the ocean.
iii) The ocean is "below" the earth, not in a subterranean sense, but in the prosaic sense that dry land is generally higher than the sea. Sea level marks the boundary between the surface of the earth, where humans dwell, and the fathomless ocean.
That interpretation is consistent with my lunar conjecture.
iv) The primary source of coastal flooding is the ocean. My lunar conjecture would ratchet that way up. It could still be wrong, but if so, it's wrong for different reasons.