In a discussion elsewhere I was told that mash thickness should be calculated with the total water volume. Even though we have that huge dead space and the grain bed is thick, it's the total water volume that matters. Apparently?
When I started checking my conversion efficiency, I saw results that backed up that claim. Check out this table at BrauKaiser:
http://braukaiser.com/wiki/index.php/Understanding_Efficiency#Measuring_conversion_efficiency
You can check conversion efficiency by taking refractometer samples over time. When I have done this, it takes about 90 minutes to get close to the theoretical maximum gravity value in that table, using thickness calculated from the total water volume. If I used a thickness value that omitted the dead space liquid, I would expect my gravity to be much higher, right? But I have never observed that.
Because my conversion efficiency approaches the theoretical maximum, I have to conclude that my efficiency problems must stem from the lauter process. But when I have tried holding back some mash water for a pour-over, it hasn't helped. Maybe I need to try a couple of gallons instead of 0.5 - 1 gal, as I have before.
Or maybe I need a mill, but I don't want to make the room for one!