AngryAdmiral

This is more an issue on the earlier ships but it's something that has always confused me. There seems to be a restriction on barbettes where you must place the small wide barbette (can't remember its exact name) first before you are allowed to place any of the other types of barbette. Why can't we just choose any barbette and must place a specific type before we can place others? It kind of limits the design of ships. Does anyone know why this is or how to get around it?