They AN/APS 20 was a fickle beast as were the engine driven generators whose output would vary with engine rpm. The radar required a stable power input that was achieved with an engine Rom of 2175. Now we never considered how the radar would operate with higher, lower, or changing rpm. It was a given that it was 2175 or nowt. Maybe 2175 gave optimum performance or lower rpm may have caused it to trip and higher to be damaged.
Whatever the facts we never queried the SOP to shut it down once we had finished our task. As for not seeing land, that is a nonsense as we used geographical features as reporting reference points. Certainly it was not effective as a mapping radar but could function as a coarse terrain warner.
Shackman has it right, .