All my anabantiods (bettas and dwarf gouramis) seem to like picking about on the bottom in hopes of a treat. With my bettas, I find that I have to 'train' them to find food on the surface-- it seems like they don't really notice it unless I draw their attention to it and even then for the first little while they spit it out a few times before swallowing it. Failing this, you can try feeding your cories Nutrafin Fry food. It sinks and is too small for bettas to eat when it falls on the gravel. Sinking wafers can be a pain though because my guys chase everyone away from them and gobble them all up and get themselves bloated
. Try wiggling your fingers, etc to make sure the food is in your betta's sight line when you feed it.