Hi LEM,
With the PMC OFF, there is more variation of thrust with airspeed and altitude changes. In most cases, the thrust decreases to below what it would be with PMC ON (assuming you set the same takeoff %N1). So, for dispatching PMC OFF, two adjustments are made. First, a new (higher) Takeoff %N1 Target is set. This partially offsets the lower thrust as the airplane accelerates and climbs. Secondly, since there is still a thrust “shortfall”, decrements have to be made to field length, climb & obstacle limit weights. These adjustments vary with OAT and the pressure altitude of the departure airport.