That is still quite a lightly planted tank, there are very few small fish that aren't happier among, or very close to, vegetation.
Have a look at <"
which fish breed....."> and <"
Splash Tetra - Copella arnoldi">
I love the Splash Tetras, really nice and interesting fish.
one studying Bronze Cory catfish coming from cover secluded spots to feed in huge groups zig zagging their way through open water and back again splitting up into smaller groups
We all know corydoras don't school....They are social fish though, so are a lot of other fish but some are true schoolers...
Based on my experience I can tell you corys do not hide or stay in secluded areas if they're happy. They're out and about...going all over the tank and if there's driftwood higher up, they'll go as high as the driftwood goes to "sniff" around. Some of mine go into the planting baskets positioned near the surface of the water.
What you don't want to see is a bunch of corys sitting tight in a corner or behind decor, etc...and not moving much....Or tetras, rasbporas or barbs sitting on one spot hiding....To illustrate what I mean, sick fish tend to detach from the "school" and sit lonely behind filters, heaters, etc....This doesn't mean that fish that hide are all sick, just trying to explain....It is very possible that some fishkeepers have never truly seen their fish being happy, especially if said fish were kept in exact same tank/conditions all the time. So what they've observed is what they think is natural for the fish....
Thankfully, due to some tank breaks, the same fish I own moved several tanks and several setups and i was able to observe behavior changes as I changed tank sizes and tank conditions....
Also, breeding is not always a sign of fish being happy. Breeding can be a surviving mechanism as my corys bred in a tank ridden with ammonia of 8ppm + that stunk the house, while their fins were literally melting in front of my eyes.....I was extremely surprised at the time. For the record I did manage to save all corys at the time and they subsequently bred again and produced offspring that survived.
Having said that, if a tank is planted to the brim, the fish will technically always be in hiding as they've got nowhere else to go....Do they like living in a tank "overstocked" with plants, I don't know....I think it very much depends on the species and what they encounter in nature....