The top image is taken with the default FSX weather engine using the realworld METAR for today 9/1
@ 1700z. The bottom image is with 3 engines running
The lower image is using Active Sky 2016 with 3 engines running. I''ve loosely tested this by turning AS16 on and off and at sea-level with engines off it does induce a very slight increase of perhaps 0.1-0.2 MP more than the FSX engine, but this seems to be more based on the difference in interpolation of weather. Testing this in the air does create swings but when power is reset to the nominal settings it still settles on being 3MP off. For note the aircraft is the new BOAC model DC6B from the Ops Center, the engine has less than 5hrs on it and are in "green" health.
I do see the signs of each engine being an individual as they all settle on their own CHT, have unique engine readings and they certainly have their own wildly different fuel flows. However, for ALL engines to be EXACTLY off by the same amount doesn't follow the pattern of the other features.