All Corydoras species feed from the substrate and they filter the substrate in their mouths and expel it via the gills. That is biological fact and there is no value in anyone arguing the opposite because it is false.
In order to provide proper nutritional food for pygmy/dwarf cories, you must use sinking foods that will sit on or in the substrate, and the fish will instinctively feed accordingly.
My last group of Corydoras pygmaeus were in a 10g tank on their own, and at one point I had 30 some cories (from six original fish). When I moved three years ago I moved them into a 29g blackwater tank, and they continued to feed from bug bites and shrimp pellets and frozen daphnia on the sand. When they were not feeding, they generally swam all over the place, browsing every plant leaf (microscopic critters in the biofilm) and hard surface, frequently "resting" on their favourite perch, the sponge filter. I suspect this was because of the food they could find there. Their behaviours were really no different than those of the 40+ larger-sized cories in the larger tank which also spent considerable time on surfaces and plant leaves. But none of these fish can find adequate food without doing what they do in the wild--filter feed from sand or silt substrates.
