When you lower boil vigor the boiloff is reduced, leaving you with a larger volume and lower OG due to the added dilution. Adjusting the boil off in your equipment profile is the proper way to bring your estimated gravity back in line with your process. BeerSmith relies on your inputs in order to properly calculate gravity, bitterness, volumes, color and various other estimated values. Any time you make a change in your process, you need to reflect it in one of the profiles you're using.