I've had my Thai silk in with various cichlids for a few months. I bought him around 2" he's now 4-5". I made sure to buy him smaller than all the others, which seems to be ok so far. His kok is starting to form.
As for aggression, he doesn't even care about the other fish.
Although they all stay clear of him (Except for feeding time) . Not sure if it's in their instincts, or he's warned them, or what?
I've never seen him attack anything, stays to himself, but he does like to bite fingers and vacuums lol Doesn't get frightened at all during maintenance.
I know it's risky, I have a 75g iso tank if he gets nasty as he grows. So far, minimal aggression.. yellows are the bullies
I also move around the caves and rocks frequently to disturb territories.