Transient Noise Simulation in Cadence Virtuoso

Hi 

I am using Cadence Virtuoso IC6.1.8-64b.83.

For a demodulator with 140GHz carrier and 40Gbps data rate, i set the transient noise with only the demodulator noise contribution ON. When i simulate it with Fmax = 700GHz, it gives higher amplitude of demodulated output signal (34mv) where as when simulated with FMax = 280GHz it gives low amplitude of the detected output signal (24 mv). I did not set Fmin so put it as default 1Hz. What is the appropriate setting in this case? Thank you