Hi Max,
yes your wright...Brochis multiuradiatus hardly takes dry food from the bottom.
Mine get about 50% frozen crustazeans as artemia, moina, daphnia and the other 30% is frozen red bloodworms and about 20% black and white moskito-larve (? what ever this is in english

). As long as I can get also living tubifex.
They also like living food, hunting for daphnias in free water ! and for moskito-larvae at the surface, mainly in the evening without light between floating plants.
There are also individuals, that take exclusively "red" food such aus red bloodworms, tubifex and living red daphnia.
What kind of bottom substrate do you use ? Be best is fine sand app. 0,1 to 0,5mm diameter. They don't like gravel very much and not like to search für food in such coarse sediments. Here the food falls into the holes between the grains...and therein it's a little dirty...theya don't like this and will probably cause fungus around ist moth and reduced barbels.
B.splendens or B.britskii is much easier to feed with dry food.
Are there other bottom dwelling species in the tank ? B.multiradiatus doesn't like that dominant inhabitants in "small" tanks...he want's to be the "king" in his area. Even smaller Corys work fine or other Brochis.
It's a nice "cory"...but itsn't easy at all.