Not a radio engineer, but it's the shape of the Faraday cage that matters I think, not the size. The required shape most likely depends on the wavelength, as the idea is to distort the waves... Basically if your grid is too tight (ie a sheet of metal) the waves keep their shape, but if the grid is too loose, the waves just pass right through.
That's what I've been told by fellow meshnet hobbyists anyhow ;)
That's what I've been told by fellow meshnet hobbyists anyhow ;)