Full power is required to counter the assumptions in contaminated performance. The published performance is not tested in those conditions; thus the performance values are approximate and that the exact type and depth of contaminant may not be known.
The effect of slush / spray impingement during takeoff is a retarding force, thus greater takeoff distances will be required. However this might help in an RTO, but then again the conditions may be inexact, the braking action incorrectly assessed/reported, and more runway already used in the takeoff roll.
Airbus view (NB this advice may be out of date, but the theory is still valid):
https://www.scribd.com/doc/167078290...inated-Runways
Slide 13 – Use maximum thrust on contaminated runways.