Sinewave Amplitude Excitation stage ADuCM350


I am currently using the software example "ImpedanceMeasurement_4WireBioIsolated" and I wanted to check what was the amplitude of the analog excitation signal. Inside the software you can define the peak amplitude of the signal in mV through the variable VPEAK. I have defined a value of 599, which is the default value for this example, and I have connected the oscilloscope to AFE8. I ran the program and the measured amplitude instead of 599mV is more or less 375mV. I tried also other values for VPEAK, but the measured amplitude it's always lower than the desired value, for example I have defined VPEAK at 399mV and measured an amplitude of 255mV. Can someone kindly explain me the reason?