I don't know it'd be the mill setting, unless he reset it tighter than you had before, whatever the factory settings were. If it's a barley crusher, of course most of us know, that those are factory set to .039". But I don't know if I'd conclude that mashing at 152 versus 148 was what gave you the higher efficiency. Either way, it's nice to get better than expected efficiency. I always get bummed out when I miss my OG by a couple points. But it's really not a big deal.