My new Upside Down Catfish isn't eating at the surface?

The first one I got fattened up right away cause it would eat at the surface and get a big belly when done, then hang on a plant upside down for awhile. The second one doesn't do that. It likes an ornament on the other side of the aquarium and is less social. he comes out after I feed them and eat the food that got in the plants. Still I am worried that is not enough. He is a little larger and I want him to fatten up a little too. Would adding a 3rd help any? Do I even have room? (you all should remember what I have... I say it enough). Will it ever start eating at the surface?