So, taking into consideration the social behaviors of betta fish, we've seen some interesting things in our years as hobbyists. Some of it's what we want to see, some of it is just really hard to explain.
Here's an example;
Acheron (red/skyblue rosetail) lived in a tank with his sibling, Manaphy (dark/navy rosetail) when they were very, very young (1-2 months old). Back when they had shorter fins and weren't so darn big.
Now, I bought Acheron when he was 3-4 months, and BB123 bought Manaphy. A month ago I recieved Manaphy and decided the brothers could share a 10g easy.
Now with the big fins both prefer a calm tank, but I need to keep it aeriated so I have bubblers and a very low filter going onthe loset setting possible, and they dont get pushed around their tanks and can easilly get their food. But as is common witht eh bigger finned boys, they'll find something to nestle against to rest from constant swimming with all that finnage.
Acheron has never rested on the bottom like this until Manaphy joined him and started using the plants as a slight hide fromt he current.