I logged on to post exactly the same thing. Except I've had my two for two months. They will eat grass and bushes and trees happily while I'm there, but when I go they do very little, (spy from my car through the day, and can see where their droppings are). They bleat a good bit, and then just curl up in the corner and wait for me to come back. If they do graze or eat its within about 20m of the gate. At the end of the day they are visibly thin (tucked up) from having barely eaten anything. I've tried the hard line, but the more hours they're in the field, the more empty they get. If it's not raining I put them outside all day.
I've tried putting them in different fields, their same field, but at the other end, feeding them half as much concentrate in the morning (with the idea that they'll be so hungry they'll have to eat), feeding them in different places in the field.
I'm thinking I may need to borrow some more goaty goats to teach them what to do!?!