It all depends on the individual from my experience. I have a senegal that is about 7-8" and he's always been kinda shy and slow to go out and eat. But I also have a 5" that is very aggressive and always hunting/foraging. I don't think the lighting is the problem, my tank is pretty well lit and the bichirs swim all over (they barely use all the hiding spots).
It might be he's just picky. Get some beefheart or other frozen treats, I'm sure he won't be able to resist.