Slitherine

A large art unit is 3 bases "large" . Where do you put the 4th attached artillery

and do attached units count for the angle of fire (so make it "larger" or do you still mesure as a "small unit" if the unit was small, or do you count it as large and what about large artillery units with attachment and angle of fire ....

I believe you add the attached gun to the side of the artillery battery so you increase its frontage. This would also count for pivots I would assume.

Never attached artillery myself as I sometimes find a large battery pretty cumbersome and too wide to deal with on its own.

The 4th base is added to the side of the existing unit - making it 4 bases wide when unlimbered.
It fires with 5 or 6 dice against all units to its front - It should fire as a small unit (without attachment) if there is a single target to the front of one of its end bases.
We saw a few 4 base units being used during early competitions, but we rarely see them now - other than historical battles - because they are too cumbersome.