SII standard fails for sharply filtered stimuli it never anticipated.

Evidence

It is worth noting that the SII standard was not designed for sharply filtered speech or sharply filtered noise such as the stimuli used in the present study. The SII is then not expected to predict the data presented here but other values for the ceiling and floor SNRs than those proposed by the standard are needed to describe speech intelligibility of sharply filtered signals. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3536