Do I understand the question correctly - are you putting the ground beef in as a custom food? Then you break it down by oz? I haven't done this myself - instead I put in a custom food and in the descrption I state the serving size there.
Dunkin Donut 1 large glazed is one serving
That's the description when I make up the custom food. With the serving size defined, if I eat half a donut, I put in 0.5 for the quanitity, or 0.33 or whatever fraction I've eaten of that food. It works pretty well.