Would you rather fight a dozen chicken sized horses or 3 horse sized chickens?
You do get 30 mins of prep time but so do your opponentz
Anyone who does not select the chicken sized horses has never been on a farm.
1) horses are cowards and making them smaller will only make that more pronounced. They might actually. Be scared to death.
2) Chickens are psychotic micro-raptors who live only for destruction. To grant them such size is madness and to fight then is hubris. Flee, flee the feathered ones for their talons are as quick as their tempers.