Do you know your values for boil off ? I don't use beer smith but I have a program that uses my equipment profile and put 0.2 gallons absorbed by grain, mash temp max 158, I think 1 gallon loss to mash tun, put the BTU rating for my burner and guessed 74% efficient and 1 gallon boil off per hour. Pretty basic values and all you have to do is measure them when you brew. I measured grain absorption by pouring into fermentor buckets and I don't sparge (80% mash efficiency) so I ignore that number.
Not sure what beer smith asks for but those are usually equipment measurements from what I've learned.