The Noahide Flood

[Huolpoch]

It'd require way much more water than that, since the earth is a sphere, and you'd need more and more water to raise the water level each subsequent inch/foot/meter/etc

radius of the earth is around 700 times greater than the depth of even a Noachian flood that drowns the tallest mountain,     so the thin shell approximation of of the volume of water that doesn’t account for what you describe  would be very close to the true volume.

The radius of the Earth doesn't really factor in.  If you have rectangular pool that requires 100 gallons of water for fill up to 1 foot in depth, it'd require  an additional 100 gallons of water to make it 2 feet in depth, another 100 gallons to make it 3 feet in dept, and so forth.  However, if the pool is in the shape of an inverted trapezoid, with a bottom narrower than the top, each subsequent foot of water depth will require more water to fill.