When you say "asian upside-down catfish", do you mean these?
Upside-Down Catfish. If so the species profile here suggests that they reach 4". I have 3 in a 75 gallon tank with a 8" tiger shovelnose and a small albino oscar. I'm well aware that one day they'll need to be moved because of the shovelnose.
If this is the type your speaking of I can't tell you much about them except the like to hide when the lights are on. However they sometimes browse for food during the day. I feed them flakes, tablets, shrimp, and an occasional treat of fresh fish. They seem pretty friendly except to eachother. They like thier own spots. When the lights are off however they will sometimes school during thier browsing.
Hoped this helped and I hope this was the type of catfish you meant.