My two that share the divided tank actually ignore eachother alot of the time. The larger one likes to flare up then retreat to his pipe, then come out again to repeat himself while the smaller one hangs out in the open more and tends to ignore the bigger one, but sometimes he joins in.

On a side note, I didn't know how BIG these guys got!! My sister had my bettas for 4 months after I moved and I couldn't believe how huge my oldest male grew, I guess I just didn't notice before when I saw them everyday!