Silent Running dilemna

After drawing a conclusion that setting Silent Running in itself has no effect, other than halting torpedo reloading, and repair operations, I tested it.

Two month patrol. 29.MAR.40 to 21.MAJ.40. Included hotspot AM53.

I never set Silent Running.
I did however, set Silent Speed (90 RPM).
I noticed no difference in my detectability, from patrols when Silent Running was set.

I've also tryed this before, both in The English Channel, and around Gibralter.
My conclussions were the same.

Does anybody know of anything in the files that contradict my findings?
I'm finding this topic to be extremely interesting.