Thanks.Not sure if this will help you but I have some Pygmies. They have cleanup duty in a fry tank with fine gravel. They seem very happy. They are not the least bit aggressive. All cory probably prefer sand but as long as it isn't sharp they seem to do fine. They were raised in gravel for decades in this hobby without a problem. Sand is still the best idea IMO.
Agree, when mine aren't just laying on the bottom resting they spend half the time in the middle third of the tank.Pygmies are more mid dwellers than bottom dwellers (unlike most cories) so it doesn't affect them as much as it would affect most other cories