Over the last few Brew Day's the brew house efficiency has been a bit lower than I'd have liked, with numbers coming in around 70% or even a little less. How the grain is crushed is probably the most important part of achieving decent efficiency. In the past the procedure I had been using involved conditioning the malt (adding a small amount of water and mixing it well, just before milling) with the theory that this should result in less damaged husks but still produce a fine crush. The crush has always looked good and I've never had a problem with sparging:
It would appear that the combination of the mill roller gap setting and conditioning the malt before crushing it was decreasing and not increasing the extract efficiency. Next Brew Day I'll run the grain through the mill without conditioning it first and hopefully notice a similar efficiency increase.