Hope this helps who? Me?
They've got a distraction at each end of the tank in the form of a reflection that won't back down. Do you think they'd still be pals, buddies, bffs 4eva if you took the mirrors away?
Squaring up to an opponent all day CAN be stressful for a betta. Am I the only one who's said it? What does that tell you?
If it works for you, great, I'm glad, but frankly I find it irresponsible of you to post "I've got two bettas in the tank and it works cos I have a mirror at each end!". For, what, 98% percent of the time, this wouldn't work out very well. Hopefully people coming across this thread from searches when when looking to see if you can keep bettas together will realise that it is really unlikely to work out and it would put their fish under more stress than is really necessary.
[The one thing my fighters do well is 'get on. and I did say 'an
Exception to the rule' I was careful to write this point. But who's to say what's in a fish mind?
If there were some magical electronic fish mind reading gadget you could plug into a fish brain maybe we'd all know for sure. So since there isn't I'm afraid it's just down to guess work and
gentle experimentation, coupled with the fact that we cause the fish stress enough capturing them..bagging and tagging then
shipping them critters half way around the world is most likely a wonder, that they may not find it quite so hard to get on in a community tank ...after all.
And I have taken the mirrors away this morning after reading comments. The results are in....No change. All is bliss in the watery depths/ Hope this helps.