I'd also definitely add some more plants. With the way yours is set up, they pretty much have no choice but to stare at each other through the divider, which will cause a lot of stress. If you look at the photo of my divided 10 gallon, I made sure to make it heavily planted, so that each betta felt safe, and not threatened by the betta being housed next to them. So far, mine do very little to no flaring, and pay little attention to the divider because all the plants give them a sense of security and plenty places to get away from the view of the other betta.