You know how all people are different, some people can eat all they want and never gain an ounce (gawd I hate them!) and some people hardly anything and immediatly gain a pound, some people have to watch what they eat constantly.
Dogs are like that too. I have one that is very thin, one that is medium build and one that is a pudge
Give him a litte more if you feel like you don't like his weight, just be careful so you don't over do it. You dont want to comprimise his health for his looks.
Let us know how it goes!