I have a gold gourami who used to be the king of the 30 g. Then I introduced a tinny blushed coy angel that grew and grew to be as big as the gold gourami. They both rule the 75 g now, but they do not bother each other.
Before changing the angel, the gourami and the other fish from the 30 to the 75 g, I added 2 dwarf flame gouramis to the big tank and let them settle in for a few weeks. Once They were all together the bullying started from the big goldie to the dwarf.
One of the dwarf died, after a few month. I think it must have been aggression because all the other fish were fine. The other dwarf is always hiding. But the aggressor is always the gold gourami, the angel is an "angel"!