A male betta with another betta, let it be females or males, will fight with each other. Its their nature. Unless they are ready to spawn, and you WANT to spawn, don't do it. I give you credit on the fact that its not smart. But a male betta will fight with any other betta no matter the size of the environment. Its scientifically proven. It cannot be done right. Because like I said a) they will fight b) the female will live in fear. Yes, some males are not the fighting type, but some females are. Most healthy and younger males will definately fight. The possibility of this working is extremely low. Why would you even want to endanger your fish's lives? Why would you want the females living in fear, causing her and the male unwanted stress that will lower their immune system making them suseptible to disease. WHY?! Geez, I don't know what to say other than that. How about this...Don't do it?! Did that get through okay? I hope so, for your fish's sakes.