Those are actually far more common and easy to find here than hasbrosus, however I have read they are far more often mid water swimmers than substrate dweller. Would you say that's true? Would that be a problem in a 20 tall with 20 ish mid to low dwelling tetras?
Corydoras pygmaeus do spend a lot of time off the substrate; they are continually browsing every surface, including plant leaves and even those close to the surface. C. hastatus is quite a mid-water swimmer. C. habrosus I had some years ago, and if memory serves me correctly they were less upper-water.
I had a bit of a search on Planet Catfish and came up with four cory species that are known to inhabit the Essquibo River system:
PlanetCatfish.com - Species Search Results
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www.planetcatfish.com
If you click on the species name, it will take you to the profile of that species.