I think the tanks are a bit to small to house a betta. Most ppl dont know that bettas are tropical fish and need a proper invironment like a ten gallon tank or even a 5 or 6 gallon.. They also need a heater. Bigger tank means bigger territorial. This will boost up bettas confidence and make him feel more prouder in flaring and showing off his fins. More space would make the betta exercise more, therefore it would help the growth of it's fins into it's maximal potential.

Betas originate from the slow moving, slightly stagnant waterways and rice fields of Southeast Asia. The oxygen content of the water in these areas is low, and the beta has evolved a secondary "labyrinth organ" to actually breathe by rising to the surface for a gulp of air. For this reason, Siamese Fighting Fish do not require the same aeration and filtration systems of most aquariums. They can live quite happily in a variety of habitats. However, just because the beta can survive in a cramped, stagnant bowl with no plants or gravel, that doesn't mean that they should be sentenced to such a life. The tiny bowls or plastic punch glasses in which these fish are sold are not suitable for long term habitation. Find a reasonably sized aquarium, goldfish bowl, or even a huge brandy snifter, and add some gravel, a live or plastic plant, and some interesting accessories. The habitat will be more interesting to you and your pet.

I suggest getting a bigger invironment for your bettas