I'd recommend setting boil off as a rate per hour not percent (which is actually the way you have it I think). It should be a fixed value depending on the pot surface area, humidity, flame, etc - not a function of how much overall volume is in the pot. Two gallon per hour for that pot seems a little high but maybe not. I boil off about 1.6 gal per hr in my 20gal pot but I know the megapots are kind of wide. Have you tested it?