I screwed up my calculation. First I used John Palmer's .25 qt/lb grain value. 10# recipe = 2.5 qts = .625 gallons. Second, my calculation forgot to convert the 2.5 quarts to .625 gallons.
My dynamic test shows the retention value of .070 qts/lb. In short, I used the wrong constant (.25qts/lb not .070 qts/lb) and I miscalculated such that the strike volume was in excess. When I lifted the bag out of the kettle/mash tun I had much more wort than I wanted. Had to do a boil off to get down to the SG and the in-the-fermentor volume I was shooting for.
Otherwise, I am sold on the process. If anybody is moving to all grain, BIAG has many advantages. The disadvantages that I see are #1 you should invest in a 15 gallon kettle/mash tun to cover the bigger grain bills, (ETA on second thought a 20# grain bill is managebale) #2 figure out where you can mash/boil and hoist a bag out of the kettle.
Edited by zymot, 11 April 2020 - 08:41 PM.