Very impressive! Sorry to say the barbettes look a little two wide.
That is the correct size for barbettes for Italian ships. That US Navy battleships or Royal Navy battleships have small barbettes compared to Italian, dosent mean everyone have to have small barbettes.
Roma class had barbettes that was bigger then the turret by a lot! some this one is based on.
the British Nelson class battleships with it's trippel 16" turrets had barbettes that was bigger then the turret.
Iowas 16" guns barbettes is also bigger, but the Americans made the turret structure, extend over the barbettes a bit more.
North Carolina class barbettes was slightly a bit bigger
Colorado class turret was made extra wide, to cover the entire barbettes, even when the gun it self only covered around half
French Richelieu-class battleships, had also quiet large barbettes for there turret.
The reason a barbettes is larger the the turret structure it self, is for spreading the weight of the turret, but also give enough space for all the equipment on the inside and also protection.
So I don't know what you are on a about, when you say the barbettes is to wide