1990 xj40 exhaust - Cat-cons

Did my car originally have a metal cover below the second set of cat-cons in the middle of the car, or was there only ever the 2-layer asbestos sandwich cover above them? I'm wondering if I should add a cover back in below to keep them hot to work better - I'm having trouble getting the NO/NO2 emissions down to an acceptable level to pass an emission test.

Best regards, Tom