Although I never was full steam ahead in corys, I did have a few that spawned in my tanks. For the most part I had very little to do with it happening. However, i did discover that the tank with sterbai would spawn when I fed them live red wigglers. This was one of my only two brief experiences feeding live. I was mostly feeding the worms to angels, diicus and clown loaches. But I would try some of the smaller worms or I would cut others in half and drop some into that cory and pleco tanks. Almost without fail about a week layer sterbai eggs would appear on the glass etc. Of I did not pull them they got eaten either by the corys or else by the Montezuma swords in the tank.
You are way much better with corys than I ever was or could be, so take this for what it may be worth. Maybe a live feeding, would help push these gys over the edge? Somehow, I think you may be feeding live already based on the great results you get with almost anything in any tank you have.
p.s. Let me know when I can mail you some Rooibos.
I do offer live chopped earthworm and mealworms
But I also offer a variety of everything, but most of my feeding regiments are bottom feeder oriented. So upper levels tend to have to adapt and most have. Very few of my fish go to the surface for the food, they follow the cories as they know when the cories go for food.
Actually given that I've got some blind fish, that's how they find food too. They can feel the cories going nuts in the water so they start nosing around the sand looking for food too. Like seeing eye fish lol
But I feed:
Live mealworms (chopped or mushed)
Live earth worms (chopped, as a treat)
OmegaOne Flakes
OmegaOne frozen goodies
Northfin Carnivore pellets (meant as feed for large carnivore monster fish, but I'll use one pellet like you would an algae wafer)
Fluval Bug Bites
Vitalis Catfish Pellets
Northfin Betta Bits
OmegaOne Shrimp Pellets
Hikari Vibrabites (a treat)
Once a month they get freeze dried tubifex or blackworms depending what I have on hand
Once a blue moon a small smidgen of frozen shrimp or smelt grated into small bite sized bits.
Midge larvae as they find in their tanks
Treats are an algae wafer or pleco Bug bite pellets, but not a main diet.
I do offer my goldfish and livebearers spirulina Flakes, occasionally give these to the bamboo shrimp and the cories steal it too.
I rotate what I feed, no set schedule but always frozen goods once or twice a week unless I'm conditioning and then I just offer as much as they'd eat every day lol.