You can detect its effect if you enter auto gently with a fixed cyclic position. Initially the nose drops as the tailplane is unstalled in the negative sense. Then the spoiler disrupts the airflow over the top of the tailplane and the nose rises again.
not totally convinced by that as generally all helicopters go nose-down when you lower the lever, just as they pitch nose up as you raise the lever. ISTR it's called instability with collective pitch or something similar.