This is a guess but the fluid dynamics likely changes? As the size of the group increases the Reynolds number probably increases making inertia a significant factor.
Individual human runners in air is maybe a bad analogy think more like honey where every stroke pushes you back as much as it pushes you forward.
This article might interest you doi.org/10.1529%2Fbiophysj.107.118257
Hawk@lemmy.dbzer0.com 10 months ago
I mean, professional cyclists do the same, as do migratory birds. Only the front has to take the resistance, the back has to spend less energy. The slow, tired ones just drop off.