2's company, 3's a crowd. Supposedly, if 3 or more aro's are together, aggression is minimized.

I guess its because there are so many, they can't tell each other apart.
I don't know about your area LFS, but the ones in my area usually have anywhere from 3-8 aro's in a tank, size is about 300g maybe, and all the fishes look good. No frayed fins or any visible bruises on the body. I asked the owner about the aro's fighting, and he said if you have 2, the probablity is much higher, but with mulitple aro's its very minimal. Also adding BW extract helps to calm everyone down.
One thing that still perplexes me is that he had 3 jars in a 250g tank with some GT's and all the fishes looked mint. The jars were around 16", the smallest one about 11-12" and none of the other fishes bugged him.
So it makes one wonder about how so many are negative about keeping aro's in a same tank, especially the jars. I guess its all a hit and miss thing, but is one willing to try?
Also, back over a decade I had a silver with a jar and they didn't fight or anything. I know I posted the pics up around here somewhere. I had the jar first, and bought the silver 2 months later. Both were relatively small at the time, but the silver grew a lot faster than the jar did.