Any idea of how Gaijin decides max range on naval weapons?

Nav weapons puts the 15inch BL Mk1 at a max range around 30km yet im sitting here in enduring confrontation waiting for ships 26km away to come into range. the wiki of course is 0 help, anyone figure out the game logic?

How do you know the 15 inch guns don’t have a maximum range of 30km?
Have you tested against a static target?

To answer the question in the topic name: Unclassified documents.