I think I got around 72 oz on my 10 gallon Commercial igloo with false bottom. I assume this needs to be addressed in the sparge, but not necessary for mashing since the sparge will wash it out.
Basically with the dead space, you don't change anything with the mash volume of water (1.25 qt/lb of grain), just add extra for the sparge?
Started brewing February 2012. Still brewing.