Agreed, he's 2" in a 4' tank by himself, the world seems very big to him. It can take over a month for a fish to really get used to a tank in my experience. I wouldn't try to feed him for a couple more days, don't want uneaten food making a mess, and he will be fine without food. Also, some dither fish would probably help him feel comfortable. This would be some danios or tetras that swim in the upper part of the tank. They may eventually be eaten by the FH, but maybe not if they are fast enough, and in the meantime they would help him feel at home.
Also- do you know about the nitrogen cycle? Is the cycle completed (0 ammonia, 0 nitrite, 1-20ppm nitrate) ? If the water parameters are not in check he will probably be stressed and not come out.