As an example,I mash 5-6lbs of grain in 2 gallons of local spring water biab style. I use a 5 gallon paint strainer bag so I can stir out the dough balls & evenly wet the grains. Then sparge with 1.5 gallons @ 165-168F for a total boil volume of 3.5G in my % gallon BK/MT. Do the boil & hop additions,chill wort & top off to 5 or 6 gallons in the FV per recipe.
I've found that stiring the grains to get out dough balls & evenly wetting them gives higher OG's.