Looks like I'm using too much water. The Braumeister calls for 23 liters, so I used 24 for my first BIAB. I was tired of having to add a lot after the boil. Now I see recommendations for 1.5 liters per pound of grain in a BIAB setup, so for 13.5 pounds (my only big beer), I get 20.25 liters. That saves me around a gallon's worth of space in the kettle during the mash, but I will definitely end up adding water afterward, if my first BIAB mash is any indication.
I never really thought about efficiency increasing with the amount of water. I figured things would just work out. Using 24 liters of water and 11 pounds of grain, I ended up with what looked like a little more than 5 gallons of wort in the fermenter, at my target OG. The gravity of the wort after moving the bag was 1.076, or around 20 points high. I had to add a gallon or so of hot water after the boil.
My efficiency made me completely happy. I know people complain about BIAB efficiency, but I got about the same amount of wort as always. Maybe because I used so much water? I used 9 pounds of Maris Otter, 2 pounds of 10L crystal malt, and for some reason, 4 ounces of table sugar. Same as always.
Beersmith predicted 1.061. Maybe I would have gotten that if I had ended up with exactly 5 gallons. I don't know exactly how much wort I had, because I filled the fermenter by eye. I left maybe 3" of space in a 6-gallon Torpedo. It may have been more than 5 gallons. Maybe some day I should put a mark inside the fermenter or kettle to tell me when I have 5 gallons, but I like going a little over to cover any losses.