Output Noise of AD5541A and AD5542A

Hello

I'm a DFAE in Japan. Our customer asks a question about AD5541A and AD5542A. Comparing the output noise spec between AD5541A and AD5542A, AD5542A is better than AD5541A. Since AD5542A has RFB and RINV, I thought that the noise would be worse because it was affected by those Johnson noises. But in reality it was the opposite. Could you please tell me the reason?

Regards,

Hiroyuki