Sometimes I wonder if the key issue to gourami aggression – and they are feisty – isn't so much space as cover, in particular thick areas of planting. I'd almost say that the aggressive fish desires this as much as the "weaker" – both need places that the less dominant fish can hide and have a smaller territory to go to. My sparklers will go through periods of coming out to joust together, sorting out who gets to mate, but they do really like thick cover and blind spots, so that they can ignore one another. They like to hide, or to be able to hide – to not have to display and engage. Adding wood, java moss, a nice thick mass of floating hydrocotyle, can all help.