A friend and I have done an exhaustive study on pre-race alcohol. While there are negatives to alcohol, there are advantages as well.
before marathon’s , 1/2 IM, and IM, we have worked our way through various alcohol options. Bear in mind we are both MOP so your mileage may vary 
1 drink (the evening before), no apparent advantages or disadvantages that we could tell
2 drinks, similarly, nothing of note either way
3 drinks, relaxed chilled out evening, telling stories of how great we used to be, sleep well except for pee breaks, race fine the next day
4 drinks, tell obvious lies about past victories, sleep like a log, sleep late, wake busting for a piss. Tear off to race and barely make the race start
5 drinks, brag to anyone who will listen, just how close we came to winning Kona, spend all night dribbling on pillow, wake, skip pre-race meal barely make race start
6+ drinks, claim to have won Kona…twice, sleep like a dead man, wake late, grab triple shot short black coffee on way to race. Forget one running shoe, and wetsuit. not worried about forgetting race food as stomach is upset anyway. Swim like hell from wave 6 trying to catch wave 3! Vomit twice, and claim you “took on water” Suffer like a rented mule on bike, trying to regain tolerance for food, and wobble on the run, drinking gallons at each aid station, shouting “I can’t believe I’m so thirsty, I drank heaps last night”
2-3 seems to be my preferred approach, but I don’t race to win, so pick your number to suit your goals.
Our research seems to concur with your findings. Glad to see peer review working so well on ST.