With doing a sparge, how do you calculate your strike water volume that you need? I do BIAB and typically your strike water is all of the water you'll need for mash and boil. I have efficiency problems as well, and am looking at solutions.
From what I've gathered, grain crush and mash pH seem to be 2 of the biggest factors in BIAB efficiency. BYO had an issue all about BIAB, and it was discussed in there (Brad Smith article I think). So if you're wanting to increase your efficiency, as others have said, it does seem like a grain mill is a great way to go.
I double crush my grains at the LBHS, but I can't seem to tell a visual difference b/w how the grains look from crush 1 to crush 2. And if you're crushing at a normal gap, instead of a tighter BIAB gap, that makes sense. for BIAB the ideal, it seems, is for the grains to almost be like flour.
Here's a link to the BYO issue, you can order it online. It was worth the purchase for me. It also discusses mash pH, and how getting it right can increase efficiency. So it seems like a grain mill and a pH meter are worthy purchases. I'm going to get a cheapo pH meter next, eventually a grain mill.
https://byo.com/stories/issue/itemlist/category/222-may-jun-2016