Much Derating above 45 degrees celsius

hi i have an omnik4 wich in my opinion is derating above a temp of 45'Celsius

i have run a test with a blower pointed at the omnik
omnik Fan test
13:37 uur ==> 2439 watt output Temperatuur 54 graden Started the Fan
13:38 uur ==> 2500 watt output
13:39 uur ==> 2580 watt output
13:40 uur ==> 2650 watt output
13:41 uur ==> 2640 watt outpput FAn off Temp 51
once the Fan was switched off the output drops to
898 watt output after 2 min it's around 2200 watt
the sky is clear at this time, nou clouds

according the specs derating should happen above 60degrees not above 45

please respond