My vote is the crush. I've made several different manifolds for my system, and the only thing that ever really affected the efficiency was the mill gap setting. Recently my efficiencies had slowly dropped from 85% down to 75%, so I checked the gap and it had drifted up to .039". So I cranked it down to around .032" (I originally had it set at .035"), and it jumped right back to 85%, with no differences in the recipe or process, and no husks in the recirculation. Beyond that, making sure the lauter is long, like 45-60min will also get you a few points (assuming he's fly sparging). I'd keep the holes many and small, and focus on the crush instead.