there seem to be an error in the way BF calculates Pre boil gravity if I have a 21ltr batch size (fermentor target) and a 5 ltr boil off with 2 ltr kettle dead space for a final gravity of 1.045 I'll have a pre boil volume of 28ltr with a gravity of 1.037 but BF shows a pre boil of 1.034. it...

Is there any way to adjust the fermentablity of different grains? eg sugars from steeped crystal which are less fermentable than sugars from malt extract