I brewed a witbier yesterday with just over 50% flaked adjuncts (~40% flaked wheat, ~10% flaked oats). My efficiency was 69%, well under what I normally achieve (I usually hit 80-85%). I didn't mill the flaked adjuncts because, well, I never have before and my efficiency hasn't suffered. But this was really the first time I've used such a high proportion of adjuncts. I'm wondering if I could expect a significant efficiency boost if I milled the flaked adjuncts to increase their surface area. I can't think of anything else in my process or in my stats from the session that would lead to such a low starting gravity.
To the extent that it would help to know my process/stats, here goes:
I milled the barley malt on my regular setting; this setting hasn't been adjusted in probably 100+ batches. This was a single infusion witbier that was mashed at 154 for 60 min. My mash pH was ~5.3-5.4. I batch sparged and collected 7.5 gallons pre-boil wort. I boiled for 90 minutes and ended up with a post-boil volume of 5.4 gallons. S.G. of the post-boil wort was 1.040 (I was shooting for 1.051). Grain bill was 4 lbs Pils, 3.75 lbs flaked wheat, 1 lb flaked oats, .30 lbs acid malt.