Ok, I believe I found the error in the published recipe, the total water called out is 24.6 quarts, and so no matter what you do you cannot end up with a pre boil wort of 6.5 gallons as you only put in 6.15 to start with. If you use the online calculator and enter all the info except the water...

https://www.brewersfriend.com/homebrew/recipe/view/180328/bill-s-double-chocolate-milk-stout

Being new to all grain brewing perhaps I do not understand the recipe, when I made this yesterday I came up with about half of the volume of wort that is shown on the Beer Stats part of the page, "6.5 gallons pre boil", when I rechecked the recipe water it called for 17.5 qts of infusion water...