Question about potential set-up with divider

I have two bettas, each in a 5.5 gallon planted blackwater set up. I have these tanks on a racking system with houseplants and decor, but I’m thinking I’d like to get rid of the bulky racking and streamline the look in the room.

That being said, I have a 20 gallon long in storage and am really leaning toward using it with a divider and housing both bettas in it.

I’ve briefly googled enough to know it can be done, but comes with risks of shared water like any other community tank. My question is though, is sight the only trigger for aggression in bettas? Or will they be able to sense each other simply by being in shared water?

Thanks in advance, and if this could have been found simply by googling another 2 or 3 minutes, forgive me haha, was hoping maybe someone has firsthand experience they can share.