[JimMorrison]

337 total provinces.

It has nothing to do with the "size". It's laid out for 12 people - and to force early wars on the land nations already. With teams in each nook, the provinces adjacent to your capital, will be adjacent to those adjacent to your partner's capital. In turn, on the other side, your adjacent provinces will touch those that are adjacent to your nearest enemy.

There are ~50 provinces in the caves. So, if one teammate gets the bottom of the nook (5 provinces), and then has no avenue to grow except the caves, he'll be able to hope to have 9 provinces before he is forced to war in order to expand.

Just seems that this sort of sardine-like layout heavily favors rush nations altogether.