Lark, I want to be sure I understand. A month ago Elwood was eating everything you gave him and yelling for more. You increased how much you give him and he is not finishing it, but will come back later and eat some more. Is that right?

Some questions in order to hopefully give you an intelligent answer.

Have you changed what you are giving him? Different brand? Same brand, different flavor. Wet vs dry?

How much more are you giving him? Most bags of dry food have guidelines how much to give them printed on the bag.

Does he look or feel like he is losing weight?

It is not unusual for cats to leave food and come back to it. Before two of mine developed health problems that require prescription food I used to just leave dry food down they could eat as they wanted.

Is he acting unwell? Using litter box normally? Activity level change?

Came back to add this... are you feeding him kitten food? Kittens should get food formulated for their needs until they are a year old.