Thought Experiment for Flat Earthers

I don't expect this to work but…

I'm not really involved with this community so I don't know with sub to post this, But it's legitimate question for flat earthers.

Would you accept the proposition that the Earth is flat but shaped like a lens, so it's a disc that is slightly elevated in the center above the edge where the ice wall would be? All the water would flow down the the edge.

If so what is the delta between the highest point (center) and lowest point (edge)?

How much of that curve would you accept?

The thought is that if I can convince them that the Earth would take that shape rather than being perfectly flat like a mirror, then just keep increasing the curve until it's… You know… A ball. But there's a starting point at least to get towards a lens shape.