Coil size to faraday cage size ratio

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Original poster: "Finn Hammer" <f-h-at-c.dk> 

All,

I`ve had my OLTC coil tested for EMI, and since it exceeds the legal limit 
a 100 times, inside a faradays cage with 50db damping. This corresponds to 
a 4Km (3miles)radius inside which the legal limit is violated.
I am going to need a better cage.

Question: For the same coil, will a big faraday cage offer better damping 
than a small one.
My reasoning says yes, since the longer distance to the cage, in the case 
of a big cage, will result in a weaker field than as in a small cage.
If the coil produces 600kV and the distance to the cage is 1meter in the 
small cage and 2 meters in the big cage, then the small cage has to damp 
from 600kV/meter, whereas the big cage only sees 300kV/meter.

Is this correct?, and will it matter? If yes, by which factor 1/2? :-|
1/4? :-\    1/16? ;-)

Cheers, Finn Hammer