Hoping this change was intended, maybe for game balance? The map & playbook has Sicily as a land theater while the alleged 'final game map' on gmtgames website shows Sicily as a naval theater.
First, Sicily was always a land theater and the artist unbidden changed it and I politely asked to have it fixed.
The combat model is obviously a simplification to accommodate a large topic in a useable format. While Sicily is technically an island, it's a big island. Just read Thucydides account of the siege and it easily fits into the model that the Syracusians won the land engagement and then won the naval battle that cut off Nicias retreat and destroyed the Athenian expedition.
That's how I wanted to model it.
I hope that makes my view clearer.