7/8 cup?!  I think most food brands recommend too much.  My 9 pound boys eat less than 3/4 cup of a 380 calorie/per cup food.     
Sam is young, and not neutered, right?  Unless his bones are visibly protruding, I wouldn't worry too much.  Just have the vet take a look and voice an opinion.     
I think I told you before that Max was not a big eater his first year.  We had to hand feed every kibble or play games putting it in the Kong.  Now he is chow hound.     
				__________________  Kristin, Max and Teddy          |