the highest mountain in the world which is roughly 30,000 feet above sea level.
That is the case in this era. Was it the case in the world that then was?
Did the flood occur on a different world?
I suspect that the oceans were a lot lower than they are now. I suspect that much of the ocean water we see now is residual water from the flood. So if anything, 6 inches per minute is a conservative estimate.
Do you think the rain that God sent to destroy the earth came down like a gentle spring shower?