Keeping a school of chromis?

[AKL1950]

I overheard my tangs and angels talking the other day. pB tang said, are you guys bored. Multiple reply’s, Yes! PB said, let’s all go chase the Chromis! And so it is in my tank. I’ve got 6 chromis and for about five months they all schooled together. Not any more. All the big fish seem to love chasing them. The Chromis usually stay out of sight in the rock structure. They all come out at feeding time, but stay hidden the rest of the day.

 

[Dar62]

I'm looking at a tank upgrade to a much larger tank, and I've always wanted to have a larger (20+) school of green chromis.
The issue is, every time I've tried groups of them (3-5) over the years, they inevitably whittle themselves down to 1 Alpha Chromis.
Has anyone had luck keeping a school? I'm hypothesizing a large enough school can dissipate the aggression enough for them to live long term.

Is this sort of a lost cause? Is the aggression inevitable at any size school?

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I have had a school of 8 chromis for about 2 years now. When I had less than 7 I had them pick on each other until there was only about 3 of them.