Discrepancy in pac and psp result

I have simulated the conversion  gain of a mixer matched to 50 ohm at both input and output. Theoretically, voltage gain and power gain should be equal because both input and output are matched to 50 ohm.

The voltage gain has been simulated using pac and power gain using psp. The power gain is 4.2dB large than voltage gain. What is the cause of this discrepancy?