To add to the over-performance problem giving unrealistic performance expectations: how often is multi engine flying training at MTOW? In my experience, not too often. And if the training is in ISA- conditions, how often is a zero thrust setting used that gives ISA+ performance? ISA-10 is rather different to ISA+20.
Finding an accurate zero thrust setting for a particular IAS & density altitude is easy. It just takes a bit of time in the air. Shut down an engine, trim to hands-off at the required speed and then restart without changing the trim. Once the engine is running set its power setting so that the aircraft is once again flying hands-off with the unchanged trim settings.