I would say that if he's maintaining his weight, and you feel that he's getting enough, he likely is.
Cali is on Go! Chicken + Turkey + Trout, and is basically free fed. I will fill her bowl later in the evening and she eats out of it as she pleases, although this is because she's not a big eater to begin with and she's always been a little too scrawny for my liking.
Moses gets 3/4 cup, twice a day of his food, and he's a not so active twelve year old dog. I convinced my mom to switch his food from Purina to Nature's Domain, and since the switch, the serving size seems much more filling.
The two and a half year old papillon. Crazy. Social butterfly. Clever.