Cranny vs Break Cranny

I'm a little confused about the cranny level VS break cranny:

I understand if I upgrade my cranny it can hold more. However, if someone attacks me and uses break cranny, they take a certain percent of what's in my cranny, correct? So wouldn't I be better off NOT upgrading my cranny so there's less they can take?

Cuz would u rather them take 50k recorces or 5k recorses

OK, so do they automatically get anything my cranny can't hold?

If they have enough troops to carry the recorses back

Your cranny holds a reserve maximum amount of 100,000 resources, so anything over that is fair game for another player to steal from you. If a player has 0 (0%) break cranny, then that 100,000 you have is safe. If a player has 10 (50%) break cranny, then only 50,000 resources are safe. It's always best to max out your cranny as it prevents your reserves from being totally depleted.