With this recipe, I wouldn't say it is the boil. I would be my money on adding the candi sugar. From my I have learned, through experience and reading/Jamil show, that adding sugar will dry a beer out and drive down the final gravity. With the belgians that I have made with adding sugar I have found the fg is extremely low. Just let it age, and you will be super suprised as to how amazing your beer is down the road.