The FADEC does not measure fuel pressure - there are no little pipes with fuel in them connected to the FADEC that can get confused. The FADEC does measure fuel flow, but it does not need this for primary control. The FADEC control system is closed loop - you demand a thrust - the valve moves to a position it thinks will give you the desired thrust. If the FADEC determines that thrust has not been achieved then it would open the valve some more until the thrust is achieved.
The only way therefore that wax / ice in the fuel arriving at the engine (discounting the fact that the two pumps and a fuel / oil heat exhanger are the first things it meets!) would confuse the FADEC is that it would keep opening the valve more and more, but would not be seeing any increase in thrust! The same would be true for any blockage to the fuel upstream of engine - it opens the valve more and more, but no more thrust is coming. The FADEC is confused in a way - but this does not cause a lack of thrust - the lack of thrust would result from the engine not getting fuel due to a blockage.
This is a fact - by the nature that the engine is controlled the FADEC cannot be corrupted by wax resulting in loss of thrust. The engine will produce a loss of thrust if it doesn't get enough fuel....
Indeed. The FADEC doesn't even have to be on the engine. Providing it gets the neccesary digital inputs it can be located anywhere on the aircraft