at operating temp, my 400e oil psi fluctuates around 1 to 1.5. during summer months when the car runs very warm..95-100 deg C, it bounces just below 1.
every 400 i test drove when looking had a bouncing gauge. seemed to be independent of mileage on cars.
the oil psi sensor is attached at the bottom of the oil filter canister. i would surmise that the fluctuation is due to the pulsation of oil through the canister at low idle