What I said is very much my opinion and my thoughts. There still isn't much factual evidence as you said, just common sense, no real right or wrong answer. All we can do is make a best guess on the experience and evidence we have to hand.Withindan518 post is pretty much the standard by which fish should be kept. The problem is though, and will always be, different hobbyists have different ideas of that "standard".
There isn't a magic formula where you can punch known variables into an algorithm and an ideal tank size pops up. It's all about eye balling it with a mix of common sense. Some of us are pretty good at it, others not so much.