I do believe the FE view of the ice wall is that it is roughly 150 ft tall and infinitely thick. Under the ice is actual rocks, but the lack of sunlight beyond the ice wall allows for an infinite plane of ice/rocks.
The problem with "lack of sunlight" beyond the ice wall is that it would get colder and colder the further away from the sun you went.
At some point it would be cold enough to turn the air into a liquid - then to freeze it solid.
But if the air froze solid - there would be a vacuum above it - into which air from the warmer regions would rush. It too would freeze. Within no much time, there would be supersonic winds rushing out over the ice wall - and within a very short time (days - not years) the air where we're living would all be gone. With no air pressure, the oceans would start to boil - and the water vapor would also rush out over the ice wall and freeze. Pretty soon, all life on Earth would be dead - there would be no air or water of any kind.
Since this CLEARLY hasn't happened - we must presume that the ice-wall malarky is nonsense. A true flat Earth would need 100 mile high walls around the edges to contain the atmosphere.