Yeah, UMich set the stimulation slightly below tactile, and in the sham period there was no electrical stimulation. But, what was communicated to participants (and to blinded clinicians) was that the sham period would either be no stimulation OR randomly timed stimulation. I believe it was communicated that way to make it even harder to unblind oneself.
That said, it wasn't perfect; during the real protocol period, once I placed the electrode a bit too high and it made my eye twitch. So, I knew there was real electrical stimulation happening, but because of how it was communicated, that alone wasn't enough to unblind me.
That said, I was fairly unblinded by week 3 because I was thinking "gee it's quiet".