I had to adjust my grain absorption a bit in BeerSmith2. It can depend on your area (dry or not) as well as your normal crush. Check where your numbers get off (After mash in, after Boil, etc) and adjust what you need to for your situation. The default numbers are close, but need to be adjusted for your particular area/equipment/situation/etc. It's under tools->Advanced. I don't remember the default, but currently have BISB Grain Absorp to 0.5000 and Grain Absorption to .9600. I think it was the BIAB setting that made the difference, but don't remember off the top of my head.