I don't think it's obvious. I do think it's obvious we should follow the GK FAQ, since it's covering the same weapon: The wound actually has to be allocated to a psyker for the psyker to take a perils.
Or we could just decide this affects psykers in a larger unit because we've all decided screamerstars suck. I'm not against that answer, actually, it's just not RAW. But I think a lot of us are coming to a "screw RAW" perspective.