Slitherine

In a normal/competition 800pt list, can you really have 16 bases of art, points total pending? I have noted the comment about field works being by mutual agreement.

Or is the intention tne immobile guns are tied to the fieldworks criteria?

You can field all 16 guns if you wish:
3 infantry divisions each of 3 infantry units - 2 with one artillery unit each and one division with 2 artillery units.
The 3x2 immobile artillery units are not under divisional command and MUST be in field fortifications.

I think the army would struggle in a 'open' battle.

It is worth noting that you cannot place field fortifications if you are the attacker. Given that artillery MUST be in fortifications, I assume that you loose them as well if attacking.
- This army would definately struggle if it 'won' the initiative roll!

Cheers
Brett

As the list say: The optional use of fortifications needs to be scenario driven.
You'd certainly be running a risk selecting the immobile fortifications for an 'open' battle, but the army is perfectly useable without it - although it will suffer from the lack of cavalry.