Power readings on the Fenix 5?

Hi, just got a pedal-based power meter a little while ago. the Favero Uno to be exact.

i noticed that the dedicated power screen gives a very steady reading when set to 3 seconds.

however, when i set one of the fields in the multi-field screen for power, the reading fluctuates wildly by up to 25-35 watts within seconds. especially when going into upper zone-2 and beyond