I Didn't Find the exact Article, but I Did find a Similar Q&A in Tropical Fish Hobbyist.
Question: Can Male Bettas Be kept together in a really large tank?
Answer: "I've seen Male bettas Kept in 20 gallon tanks together. With no Perceptible Fighting, So it's certainly Possible."
"To understand the situation, You need to know that we don't have the regular fighting Strain over here, At least that is not what is generally sold in the fish shops."
"The Siamese Originally kept these little fish and selectively bred them for their fighting propensities. They were placed in a clay pot, and the first fish to give way was the loser. Only the winners were bred, so the more tenacious and pugnacious Males influence was perpetuated and intensified. However, many years ago, Americans and Europeans Began breeding the fish for Long fins and bright colors. While the fighting instinct was not selected, it has persisted to some degree, One reason for keeping the males separate during the grow out period, is just to keep the fins in perfect shape."
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I Also found an article that stated Keeping Males in close proximity to each other in clear cups Like at walmart, Is training them to be more aggressive, and that a Male betta that has never seen Another male betta would not even know what to do, and in this article it also stated that they have Kept Male bettas together with No fighting.